CVE-2020-1730
libssh: denial of service when handling AES-CTR (or DES) ciphers
Severity
ModerateRed Hat Product Security
CVSS 3.1
Review impact separately from score.
Published · April 9, 2020
Updated · November 21, 2025
Description
A flaw was found in the way libssh handled AES-CTR (or DES ciphers if enabled) ciphers. The server or client could crash when the connection hasn't been fully initialized and the system tries to cleanup the ciphers when closing the connection. The biggest threat from this vulnerability is system availability.
CVSS score applicability
The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.
Mitigation
Disable AES-CTR ciphers (and DES in libssh 0.8). If you implement a server using libssh we advise to use a prefork model so each session runs in an own process. If you have implemented your server this way this is not really an issue. The client will kill its own connection.
CVSS / CWE
CVSS 3.1 · 5.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CWE-476 · NULL Pointer Dereference