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VulnerabilityPublished Updated

Dvc: AsyncSSH vulnerable to Prefix Truncation Attack (a.k.a

Affects dvcSource GCVE Database

0

CVSS 5.9 Medium : upgrade to 3.33.4_1 when convenient.

Data as of 26 Oct 2026, 16:20 UTC

CVSS 3.1 base score
5.9Medium
How severe the flaw is on the 0–10 CVSS scale.
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:N

What to do

Upgrade dvc to 3.33.4_1.

Affected software

ProductAffectedFixed in
Homebrewdvcpkg:brew/dvcOther threatsAffected
  • >=2.7.3_1 <3.33.4_1
Fixed in
  • 3.33.4_1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

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

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