Vision
16 Sep
## min read

Vulnerabilities patched in Aztec 2.0

Aztec 2.0's recent security enhancements address key vulnerabilities, bolstering trust and safety in the network.

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Written by
Zac Williamson
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In March 2021, we launched Aztec 2.0, which enables users to shield and send funds privately through Aztec private rollups. Aztec 2.0 utilizes our state of the art zkSNARK proving system, PLONK, developed in-house for the express purpose of scaling Ethereum with strong user privacy guarantees.

Aztec 2.0 is built with bleeding-edge cryptography and it is critical to promptly address any bugs. Aztec is in a continual state of audit internally and externally, incentivized by a bug bounty with Immunefi. Our core team discovered two security vulnerabilities as part of our internal efforts, with special thanks to our chief scientist Ariel Gabizon. Community members Sean Bowe and Daira Hopwood also highlighted vulnerabilities.

Transparency is important to us. We want our users to trust our technology not because nobody can understand it, but because anybody can understand it. In this post, we discuss the bugs discovered in Aztec 2.0 after deployment. These security vulnerabilities have been patched and we are confident no user funds have been lost.

Bugs found and addressed pre-launch

See also bugs previously reported in this post.

Bug: Pedersen hash input checks

We use Pedersen hashes inside our circuits when a collision-resistant hash function is required (i.e. when the hash function does not need to be modelled as a random oracle).

When performing a Pedersen hash in TurboPlonk, the binary representation of each input field element is split into 128 2-bit windows, whose sum is equal to the input.

Each window is used to index a 2-bit lookup table of elliptic curve generator points, which are summed together to produce the Pedersen hash output.

The bug was that, when validating the sum of the windows equalled the input field element, we were validating this [mod p], where p is the native circuit modulus.

This meant that every hash input effectively had two possible representations in 2-bit window form (the actual binary value or the value + [p]). This meant that every Pedersen hash effectively had two different outputs.

A consequence of this bug is that it was possible to generate two nullifiers for every note. This would enable a double-spending attack.

Action Taken

Our circuits were updated to always validate the sum of Pedersen hash input 2-bit windows were [< p], when required.

Risks to Users

None. This bug was identified and fixed before we launched.

Bugs found and patched post-launch

Bug: Merkle root position check

The rollup contains a “root” tree; a Merkle tree containing the past Merkle roots of the note tree (which contains all join-split “value” notes and user “account” notes).

As part of the root rollup circuit, the rollup provider must compute the new root of the note tree and insert it into the root tree. The intended position of the new leaf in the tree is directly adjacent to the rightmost non-zero leaf; i.e. the tree is initialized to all zero leaves, and then updated from left-to-right.

The bug was that our circuit did not actually constrain the position of the new leaf. In reality, the rollup provider could have inserted the new leaf at *any* position in the root tree. An adversary would have been able to insert a leaf at an arbitrary location in the root tree and not reveal the location (this location is not a public input).

If after such an insertion the adversary doesn’t participate in future rollup creation, from that point on *nobody else* can create a valid rollup and the system is frozen and unable to process for any future transactions.

Action taken

The root rollup circuit was modified to validate leaves inserted into the root tree are at the correct position. The rollup smart contract was updated to use the verification keys from the new circuit.

Risks to users

In theory, a malicious actor had two months to find and exploit this bug. However, the only entity able to launch this attack was the rollup provider. Currently, only Aztec can create and submit rollup proofs.

We confirmed there was no attack by reconstructing the data root tree and validating there are no out-of-position leaves.

Bug: Recursive proof verification

When aggregating private transactions in our rollup circuit, we use the following circuit structure:

Join-split Circuit: Executes a private transaction; generated by the user locally on their device.

Rollup Circuit: Verifies the correctness of 28 join-split circuit proofs and performs database updates into the rollup’s Merkle trees.

Root Rollup Circuit: Verifies the correctness of 4 rollup circuit proofs.When verifying a Plonk proof inside one of our circuits, partial verification and proof aggregation occurs.Each proof is verified up to the point that a bilinear pairing check is required. The Plonk verification algorithm’s bilinear pairing check is structured such that both G2 group elements are fixed and do not vary between different proofs.

Instead of performing this pairing check inside our root rollup circuit, these two group elements are defined to be public inputs of the root rollup circuit. i.e. they are broadcasted on-chain as part of the root rollup proof.

The verifier smart contract will then extract the two group elements and aggregate them into the pairing check computed by the smart contract.

The bug was that, when performing the proof aggregation step in the root rollup circuit, we were aggregating only the rollup proofs, but not the join-split proofs.

Action Taken

The root rollup circuit was modified to correctly aggregate join-split circuit proofs. The rollup smart contract was updated to use the verification keys from the new circuit.

Risks to Users

This bug enables an adversary to generate fake join-split proofs (e.g. double spend transactions). This would not have been picked up by either the rollup circuit logic or the verifier smart contract logic. If an attacker generated a fake join-split proof, they would need to convince a rollup provider to include their malicious proof in a rollup circuit proof.

Aztec is currently the only rollup provider and we use our falafel software library to validate the correctness of every join-split proof included in a rollup. The verification logic in falafel was not affected by this bug. As a result, we are confident that no malicious proofs were included in any rollup block because of this bug

Bug: Generating randomness

When generating random secrets, a Mersenne Twister was being used with a random seed. The determinism of the twister made this unsuitable as all random variables produced in a proof could be determined with knowledge of one of them. This issue should not have affected the generation of user secrets and private keys.

Action Taken

The Mersenne Twister was removed. Random number generation is delegated to the base operating system. On the web, this is done via the WebCrypto API.

Risks to Users

This bug affected random numbers generated in two instances:

  • Users creating privacy proofs
  • Rollup providers creating rollup proofs

The rollup proof does not have to be zero-knowledge as no secret information is hidden (privacy is achieved entirely via the privacy proof).

When constructing a privacy proof, several random variables are generated as blinding factors. If any of these leak, then it is possible to recover the remaining randomness using this bug and remove the blinding factors from the proof. In theory, this would allow an attacker to recover user secrets and private keys.

It is expected that no random variables are leaked when generating a proof. If a variable is leaked, the user’s device is compromised and it is likely an attacker has access to all 12 random variables regardless.

Bug: Generating prime field elements

When generating random 254-bit prime field elements, a random 256-bit number was generated and then truncated modulo the field order. This produces random numbers where smaller values have a significant positive bias.

Risks to Users

Notes and nullifiers generated prior to May 6th will be marginally easier to decipher via brute-force attacks. Such attacks are still not remotely practical and we are confident that users affected by this issue do not need to regenerate their Aztec private keys.

Action Taken

Random field elements are now generated via creating a 512-bit number and reducing modulo the field modulus. This largely eliminates any bias in the resulting field element.

The last two issues were found with the help of Daira Hopwood and Sean Bowe from the Electric Coin Company. They will both receive zkETH as a thanks for their help.

Bug: Not checking decrypted note details match insertion to tree

During a transaction, a recipient receives the details of their new note in an encrypted message. We weren’t checking that the commitment added to the note tree indeed corresponds to these note details.

Risks to Users

An attacker could have made the user think they received funds that were not really sent. Only when trying to spend the funds using the decrypted note details, would the user realize the problem.

Action Taken

In our code update from May 6th, we added the required checks in our client software that validates viewing keys map to legitimate notes in the Aztec state tree.

We developed PLONK in order to bring scalable privacy to Ethereum. As the team behind this breakthrough cryptography, we take our responsibility to the security of users’ funds and user privacy very seriously. Particularly during these early deployment stages, we will continuously audit and patch the code as necessary.

While we have an incredibly talented core team, we don’t expect that potential vulnerabilities will solely be detected internally. Community members are an essential part of our development process.

We welcome your feedback and contributions to our auditing efforts.

➡️ Get in touch with our team on Discord.

Our currently deployed code can be found on our bug bounty repository.

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Aztec Network
Aztec Network
31 Mar
xx min read

Announcing the Alpha Network

Alpha is live: a fully feature-complete, privacy-first network. The infrastructure is in place, privacy is native to the protocol, and developers can now build truly private applications. 

Nine years ago, we set out to redesign blockchain for privacy. The goal: create a system institutions can adopt while giving users true control of their digital lives. Privacy band-aids are coming to Ethereum (someday), but it’s clear we need privacy now, and there’s an arms race underway to build it. Privacy is complex, it’s not a feature you can bolt-on as an afterthought. It demands a ground-up approach, deep tech stack integration, and complete decentralization.

In November 2025, the Aztec Ignition Chain went live as the first decentralized L2 on Ethereum, it’s the coordination layer that the execution layer sits on top of. The network is not operated by the Aztec Labs or the Aztec Foundation, it’s run by the community, making it the true backbone of Aztec. 

With the infrastructure in place and a unanimous community vote, the network enters Alpha. 

What is the Alpha Network?

Alpha is the first Layer 2 with a full execution environment for private smart contracts. All accounts, transactions, and the execution itself can be completely private. Developers can now choose what they want public and what they want to keep private while building with the three privacy pillars we have in place across data, identity, and compute.

These privacy pillars, which can be used individually or combined, break down into three core layers: 

  1. Data: The data you hold or send remains private, enabling use cases such as private transactions, RWAs, payments and stablecoins.
  2. Identity: Your identity remains private, enabling accounts that privately connect real world identities onchain, institutional compliance, or financial reporting where users selectively disclose information.
  3. Compute: The actions you take remain private, enabling applications in private finance, gaming, and beyond.

The Key Components  

Alpha is feature complete–meaning this is the only full-stack solution for adding privacy to your business or application. You build, and Aztec handles the cryptography under the hood. 

It’s Composable. Private-preserving contracts are not isolated; they can talk to each other and seamlessly blend both private and public state across contracts. Privacy can be preserved across contract calls for full callstack privacy. 

No backdoor access. Aztec is the only decentralized L2, and is launching as a fully decentralized rollup with a Layer 1 escape hatch.

It’s Compliant. Companies are missing out on the benefits of blockchains because transparent chains expose user data, while private networks protect it, but still offer fully customizable controls. Now they can build compliant apps that move value around the world instantly.

How Apps Work on Alpha 

  1. Write in Noir, an open-source Rust-like programming language for writing smart contracts. Build contracts with Aztec.nr and mark functions private or public.
  1. Prove on a device. Users execute private logic locally and a ZK proof is generated.
  1. Submit to Aztec. The proof goes to sequencers who validate without seeing the data. Any public aspects are then executed.
  1. Settle on Ethereum. Proofs of transactions on Aztec are settled to Ethereum L1.

Developers can explore our privacy primitives across data, identity, and compute and start building with them using the documentation here. Note that this is an early version of the network with known vulnerabilities, see this post for details. While this is the first iteration of the network, there will be several upgrades that secure and harden the network on our path to Beta. If you’d like to learn more about how you can integrate privacy into your project, reach out here

To hear directly from our Cofounders, join our live from Cannes Q&A on Tuesday, March 31st at 9:30 am ET. Follow us on X to get the latest updates from the Aztec Network.

Aztec Network
Aztec Network
27 Mar
xx min read

Critical Vulnerability in Alpha v4

On Wednesday 17 March 2026 our team discovered a new vulnerability in the Aztec Network. Following the analysis, the vulnerability has been confirmed as a critical vulnerability in accordance with our vulnerability matrix.

The vulnerability affects the proving system as a whole, and is not mitigated via public re-execution by the committee of validators. Exploitation can lead to severe disruption of the protocol and theft of user funds.

In accordance with our policy, fixes for the network will be packaged and distributed with the “v5” release of the network, currently planned for July 2026.

The actual bug and corresponding patch will not be publicly disclosed until “v5.”

Aztec applications and portals bridging assets from Layer 1s should warn users about the security guarantees of Alpha, in particular, reminding users not to put in funds they are not willing to lose. Portals or applications may add additional security measures or training wheels specific to their application or use case.

State of Alpha security

We will shortly establish a bug tracker to show the number and severity of bugs known to us in v4. The tracker will be updated as audits and security researchers discover issues. Each new alpha release will get its own tracker. This will allow developers and users to judge for themselves how they are willing to use the network, and we will use the tracker as a primary determinant for whether the network is ready for a "Beta" label.

Additional bug disclosure

We have identified a vulnerability in barretenberg allowing inclusion of incorrect proofs in the Aztec Network mempool, and ask all nodes to upgrade to versions v.4.1.2 or later.

We’d like to thank Consensys Diligence & TU Vienna for a recent discovery of a separate vulnerability in barretenberg categorized as medium for the network and critical for Noir:

We have published a fixed version of barretenberg.

We’d also like to thank Plainshift AI for discovery, reproduction, and reporting of one more vulnerability in the Aztec Network and their ongoing work to help secure the network.

Aztec Network
Aztec Network
18 Mar
xx min read

How Aztec Governance Works

Decentralization is not just a technical property of the Aztec Network, it is the governing principle. 

No single team, company, or individual controls how the network evolves. Upgrades are proposed in public, debated in the open, and approved by the people running the network. Decentralized sequencing, proving, and governance are hard-coded into the base protocol so that no central actor can unilaterally change the rules, censor transactions, or appropriate user value.

The governance framework that makes this possible has three moving parts: Aztec Improvement Proposal (AZIP), Aztec Upgrade Proposal (AZUP), and the onchain vote. Together, they form a pipeline that takes an idea to a live protocol change, with multiple independent checkpoints along the way.

The Virtual Town Square

Every upgrade starts with an AZIP. AZIPs are version-controlled design documents, publicly maintained on GitHub, modeled on the same EIP process that has governed Ethereum since its earliest days. Anyone is encouraged to suggest improvements to the Aztec Network protocol spec.

Before a formal proposal is opened, ideas live in GitHub Discussions, an open forum where the community can weigh in, challenge assumptions, and shape the direction of a proposal before it hardens into a spec. This is the virtual town square: the place where the network's future gets debated in public, not decided behind closed doors.

The AZIP framework is what decentralization looks like in practice. Multiple ideas can surface simultaneously, get stress-tested by the community, and the strongest ones naturally rise. Good arguments win, not titles or seniority. The process selects for quality discussion precisely because anyone can participate and everything is visible.

Once an AZIP is formalized as a pull request, it enters a structured lifecycle: Draft, Ready for Discussion, then Accepted or Rejected. Rejected AZIPs are not deleted — they remain permanently in the repository as a record of what was tried and why it was rejected. Nothing gets quietly buried.

Security Considerations are mandatory for all Core, Standard, and Economics AZIPs. Proposals without them cannot pass the Draft stage. Security is structural, not an afterthought.

From Proposal to Upgrade

Once Core Contributors, a merit-based and informal group of active protocol contributors, have reviewed an AZIP and approved it for inclusion, it gets bundled into an AZUP.

An AZUP takes everything an AZIP described and deploys it — a real smart contract, real onchain actions. Each AZUP includes a payload that encodes the exact onchain changes that will occur if the upgrade is approved. Anyone can inspect the payload on a block explorer and see precisely what will change before voting begins.

The payload then goes to sequencers for signaling. Sequencers are the backbone of the network. They propose blocks, attest to state, and serve as the first governance gate for any upgrade. A payload must accumulate enough signals from sequencers within a fixed round to advance. The people actually running the network have to express coordinated support before any change reaches a broader vote.

Once sequencers signal quorum, the proposal moves to tokenholders. Sequencers' staked voting power defaults to "yea" on proposals that came through the signaling path, meaning opposition must be active, not passive. Any sequencer or tokenholder who wants to vote against a proposal must explicitly re-delegate their stake before the voting snapshot is taken. The system rewards genuine engagement from all sides.

For a proposal to pass, it must meet quorum, a supermajority margin, and a minimum participation threshold, all three. If any condition is unmet, the proposal fails.

Built-In Delays, Built-In Safety

Even after a proposal passes, it does not execute immediately. A mandatory delay gives node operators time to deploy updated software, allows the community to perform final checks, and reduces the risk of sudden uncoordinated changes hitting the network. If the proposal is not executed within its grace period, it expires.

Failed AZUPs cannot be resubmitted. A new proposal must be created that directly addresses the feedback received. There is no way to simply retry and hope for a different result.

No Single Point of Control

The teams building the network have no special governance power. Sequencers, tokenholders, and Core Contributors are the governing actors, each playing a distinct and non-redundant role.

No single party can force or block an upgrade. Sequencers can withhold signals. Tokenholders can vote nay. Proposals not executed within the grace period expire on their own.

This is decentralization working as intended. The network upgrades not because a team decides it should, but because the people running it agree that it should.

If you want to help shape what Aztec becomes, the forum is open. The proposals are public. The town square is yours. 

Follow Aztec on X to stay up to date on the latest developments.

Aztec Network
Aztec Network
10 Mar
xx min read

Alpha Network Security: What to Expect

Aztec’s Approach to Security

Aztec is novel code — the bleeding edge of cryptography and blockchain technology. As the first decentralized L2 on Ethereum, Aztec is powered by a global network of sequencers and provers. Decentralization introduces some novel challenges in how security is addressed; there is no centralized sequencer to pause or a centralized entity who has power over the network. The rollout of the network reflects this, with distinct goals at each phase.

Ignition

Validate governance and decentralized block building work as intended on Ethereum Mainnet. 

Alpha

Enable transactions at 1TPS, ~6s block times and improve the security of the network via continual ongoing audits and bug bounty. New releases of the alpha network are expected regularly to address any security vulnerabilities. Please note, every alpha deployment is distinct and state is not migrated between Alpha releases. 

Beta

We will transition to Beta once the network scales to >10 TPS, with reduced block times while ensuring 99.9% uptime. Additionally, the transition requires no critical bugs disclosed via bug bounty in 3 months. State migrations across network releases can be considered.

TL;DR: The roadmap from Ignition to Alpha to Beta is designed to reflect the core team's growing confidence in the network's security.

This phased approach lets us balance ecosystem growth while building security confidence and steadily expanding the community of researchers and tools working to validate the network’s security, soundness and correctness.

Ultimately, time in production without an exploit is the most reliable indicator of how secure a codebase is.

At the start of Alpha, that confidence is still developing. The core team believes the network is secure enough to support early ecosystem use cases and handle small amounts of value. However this is experimental alpha software and users should not deposit more value than they are willing to lose. Apps may choose to limit deposit amounts to mitigate risk for users.

Audits are ongoing throughout Alpha, with the goal to achieve dual external audits across the entire codebase.

The table below shows current security and audit coverage at the time of writing.

The main bug bounty for the network is not yet live, other than for the non-cryptographic L1 smart contracts as audits are ongoing. We encourage security researchers to responsibly disclose findings in line with our security policy .

As the audits are still ongoing, we expect to discover vulnerabilities in various components. The fixes will be packaged and distributed with the “v5” release.

If we discover a Critical vulnerability in “v4” in accordance with the following severity matrix, which would require the change of verification keys to fix, we will first alert the portal operators to pause deposits and then post a message on the forum, stating that the rollup has a vulnerability.

Security of the Aztec Virtual Machine (AVM)

Aztec uses a hybrid execution model, handling private and public execution separately — and the security considerations differ between them.

As per the audit table above, it is clear that the Aztec Virtual Machine (AVM) has not yet completed its internal and external audits. This is intentional as all AVM execution is public, which allows it to benefit from a “Training Wheel” — the validator re-execution committee.

Every 72 seconds, a collection of newly proposed Aztec blocks are bundled into a "checkpoint" and submitted to L1. With each proposed checkpoint, a committee of 48 staking validators randomly selected from the entire set of validators (presently 3,959) re-execute all txs of all blocks in the checkpoint, and attest to the resulting state roots. 33 out of 48 attestations are required for the checkpoint proposal to be considered valid. The committee and the eventual zk proof must agree on the resultant state root for a checkpoint to be added to the proven chain. As a result, an attacker must control 33/48 of any given committee to exploit any bug in the AVM.

The only time the re-execution committee is not active is during the escape hatch, where the cost to propose a block is set at a level which attempts to quantify the security of the execution training wheel. For this version of the alpha network, this is set a 332M AZTEC, a figure intended to approximate the economic protection the committee normally provides, equivalent to roughly 19% of the un-staked circulating supply at the time of writing. Since the Aztec Foundation holds a significant portion of that supply, the effective threshold is considerably higher in practice.

Quantifying the cost of committee takeover attacks

A key design assumption is that just-in-time bribery of the sequencer committee is impractical and the only ****realistic attack vector is stake acquisition, not bribery.

Assuming a sequencer set size of 4,000 and a committee that rotates each epoch (~38.4mins) from the full sequencer set using a Fisher-Yates shuffle seeded by L1 RANDAO we can see the probability and amount of stake required in the table below.

To achieve a 99% probability of controlling at least one supermajority within 3 days, an attacker would need to control approximately 55.4% of the validator set - roughly 2,215 sequencers representing 443M AZTEC in stake. Assuming an exploit is successful their stake would likely de-value by 70-80%, resulting in an expected economic loss of approximately 332M AZTEC.

To achieve only a 0.5% probability of controlling at least one supermajority within 6 months, an attacker would need to control approximately 33.88% of the validator set.

What does this means for builders?

The practical effect of this training wheel is that the network can exist while there are known security issues with the AVM, as long as the value an attacker would gain from any potential exploit is less than the cost of acquiring 332M AZTEC.

The training wheel allows security researchers to spend more time on the private execution paths that don’t benefit from the training wheel and for the network to be deployed in an alpha version where security researchers can attempt to find additional AVM exploits.

In concrete terms, the training wheel means the Alpha network can reasonably secure value up to around 332M AZTEC (~$6.5M at the time of writing).

Ecosystem builders should keep the above limits in mind, particularly when designing portal contracts that bridge funds into the network.

Portals are the main way value will be bridged into the alpha network, and as a result are also the main target for any exploits. The design of portals can allow the network to secure far higher value. If a portal secures > 332M AZTEC and allows all of its funds to be taken in one withdrawal without any rate limits, delays or pause functionality then it is a target for an AVM exploit attack.

If a portal implements a maximum withdrawal per user, pause functionality or delays for larger withdrawals it becomes harder for an attacker to steal a large quantum of funds in one go.

Conclusion

The Aztec Alpha code is ready to go. The next step is for someone in the community to submit a governance proposal and for the network to vote on enabling transactions. This is decentralization working as intended.

Once live, Alpha will run at 1 TPS with roughly 6 second block times. Audits are still ongoing across several components, so keep deposits small and only put in what you're comfortable losing.

On the security side, a 48-validator re-execution committee provides the main protection during Alpha, requiring 33/48 consensus on every 72-second checkpoint. Successfully attacking the AVM would require controlling roughly 55% of the validator set at a cost of around 332M AZTEC, putting the practical security ceiling at approximately $6.5M.

Alpha is about growing the ecosystem, expanding the security of the network, and accumulating the one thing no audit can shortcut: time in production. This is the network maturing in exactly the way it was designed to as it progresses toward Beta.