CVE-2026-56855: CWE-770: Allocation of Resources Without Limits or Throttling in golang.org/x/crypto golang.org/x/crypto/ssh
Description
CVE-2026-56855 is a high-severity vulnerability in the golang.org/x/crypto/ssh package that allows a malicious peer to cause a deadlock in an SSH connection by sending crafted messages after the SSH channel is established. The issue arises because the package buffers unexpected messages instead of treating them as protocol errors, leading to blocking behavior. The vulnerability is addressed by explicitly handling all RFC 4254 channel messages and terminating connections upon receiving unexpected messages.
CVSS v3.1
Score 7.5high
Affected software
golang.org/x/crypto
golang.org/x/crypto/ssh
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Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2026-56855) in golang.org/x/crypto/ssh involves allocation of resources without limits or throttling, specifically due to buffering unexpected SSH channel messages rather than treating them as protocol errors. This behavior can cause the entire SSH connection to deadlock when a malicious peer sends crafted messages after channel establishment. The fix requires explicit handling of all RFC 4254 channel messages and tearing down connections on unexpected messages to prevent blocking.
Potential Impact
The vulnerability can cause a denial of service by deadlocking the entire SSH connection, impacting availability. There is no impact on confidentiality or integrity reported. No known exploits in the wild have been identified.
Mitigation Recommendations
A fix is available that explicitly handles all RFC 4254 channel messages and tears down connections on unexpected messages. Users should upgrade to golang.org/x/crypto/ssh version 0.56.0 or later to remediate this issue. Patch status is confirmed by the affectedVersions data indicating versions before 0.56.0 are vulnerable.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- Go
- Date Reserved
- 2026-06-23T15:10:49.353Z
- State
- PUBLISHED
Threat ID: 6a987e89acd9273b49a9f1aa
Added to database: 09/02/2026, 19:52:41 UTC
Last enriched: 10/18/2026, 00:35:45 UTC
Last updated: 10/18/2026, 00:35:45 UTC
Views: 182
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