CVE-2026-56855
UnknownSummary
After a channel is established, a malicious peer could send crafted messages causing a deadlock of the entire connection. Now all RFC 4254 channel messages are handled, and global requests are explicitly processed. Other messages are treated as protocol errors and the connection is torn down instead of buffering and blocking.
Risk Assessment
An attacker can cause a permanent connection deadlock, leading to denial of service or resource exhaustion.
Recommendation
Update the library to a patched version that prevents deadlocks and properly handles protocol errors.
Other vulnerabilities in SSH library
See all- CVE-2026-39834Critical
When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused an infinite loop sending empty packets. The fix uses int64 for size comparison to prevent truncation.
- CVE-2026-39830Critical
In an SSH library (likely Go), a malicious SSH peer can send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine cannot be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.
Original NVD description (English source)
Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all other messages as a protocol error and tear the connection down instead of buffering and blocking.