Dvc: AsyncSSH vulnerable to Prefix Truncation Attack (a.k.a
Affects dvcSource GCVE Database
CVSS 5.9 Medium : upgrade to 3.33.4_1 when convenient.
Data as of 26 Oct 2026, 16:20 UTC
- Patch
- Available – fixed in 3.33.4_1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:NWhat to do
Upgrade dvc to 3.33.4_1.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewdvcpkg:brew/dvcOther threats | Affected
| Fixed in
|
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AI-suggested
A patch is available that adds support for a 'strict kex' handshake to prevent the prefix truncation attack. Both client and server must support this countermeasure for it to be effective. As a temporary measure, disabling the affected algorithms (ChaCha20-Poly1305 and Encrypt-then-MAC with CBC ciphers) and using unaffected alternatives like AES-GCM is recommended until patches are applied.
Description
AsyncSSH versions 2.14.1 and earlier are vulnerable to a prefix truncation attack (Terrapin attack) targeting the ChaCha20-Poly1305 and Encrypt-then-MAC SSH algorithms. This attack allows a man-in-the-middle to strip messages after the initial key exchange, breaking SSH extension negotiation and downgrading connection security. The vulnerability exploits the lack of authentication for SSH_MSG_IGNORE messages and sequence number checks only after key exchange. The attack is guaranteed to work on ChaCha20-Poly1305 and requires CBC ciphers for practical exploitation of Encrypt-then-MAC. A patch is available that implements a 'strict kex' handshake to prevent this attack, requiring support on both client and server sides. As a temporary mitigation, disabling affected algorithms and using alternatives like AES-GCM is recommended.
References
- github.com/ronf/asyncssh/security/advisories/GHSA-hfmc-7525-mj55 (opens in a new tab)
- github.com/ronf/asyncssh/commit/0bc73254f41acb140187e0c89606311f88de5b7b (opens in a new tab)
- github.com/ronf/asyncssh/commit/69f5a41b458b29367a65fe469c2b0255b5db210a (opens in a new tab)
- github.com/ronf/asyncssh (opens in a new tab)