CVE-2026-39834
CriticalCVSS 9.1Exploitation Probability (EPSS)
Low risk38th percentile - higher than 38% of all known CVEs
Summary
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.
Risk Assessment
An attacker could cause a denial of service by sending a large data packet, leading to an infinite loop and resource exhaustion on the SSH server.
Recommendation
Update the SSH library to a version that uses int64 for payload size calculation.
Other vulnerabilities in SSH library
See all- 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.
- CVE-2026-56855High
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.
Original NVD description (English source)
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 the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS