RUSTSEC-2026-0211 Non-constant time Authentication Tag Check in AES-GCM Decryption
Timing side-channel in AES-GCM tag check allows attackers to recover authentication tags and forge ciphertexts via decryption oracles.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is RUSTSEC-2026-0211?
RUSTSEC-2026-0211 is a vulnerability in libcrux-aesgcm, published on 14 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
AES-GCM decryption used an implementation for checking the provided
authentication tag against the recomputed authentication tag that was
intended to be constant-time, but resulted in non-constant-time code
generation in certain circumstances.
Note that libcrux-aesgcm does not give guarantees on constant-time
code generation and possible mitigations must be considered
on a best-effort basis.
Impact
Users of libcrux-aesgcm that expose a decryption oracle to an
attacker, which allows repeatedly querying for the same ciphertext
were at risk from timing side-channel attacks, depending on their
compilation environment. In the worst case, this could lead to
recovery of the recomputed authentication tag by the attacker, which
enables ciphertext forgery.
Mitigation
Starting from version 0.0.9 (published as [email protected]),
AES-GCM decryption uses a different, best-effort constant-time
implementation of the tag check, which has been checked to reliably
lead to constant time code generation, at the moment.
Which versions are affected by RUSTSEC-2026-0211?
1 open source package ship an affected version, including libcrux-aesgcm.
| Package | Affected | Fixed in |
|---|---|---|
libcrux-aesgcm crates.io | From 0.0.0-0 | None |
How do I fix RUSTSEC-2026-0211?
No fix has been published for RUSTSEC-2026-0211 yet. Limit exposure of the affected software until one is available.
Is RUSTSEC-2026-0211 being exploited?
There is no known exploitation of RUSTSEC-2026-0211 in the wild and no public exploit code.