phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()
8Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 3.7epss 0.4%
exploitation probability
0.4%top 71% of all CVEs
observed exploitation
nono source reports it
phpseclib is a PHP secure communications library. Starting in 0.1.1 and prior to 3.0.51, 2.0.53, and 1.0.28, phpseclib\Net\SSH2::get_binary_packet() uses PHP's != operator to compare a received SSH packet HMAC against the locally computed HMAC. != on equal-length binary strings in PHP uses memcmp(), which short-circuits on the first differing byte. This is a real variable-time comparison (CWE-208), proven by scaling benchmarks. This vulnerability is fixed in 3.0.51, 2.0.53, and 1.0.28.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Affected products
phpseclib · phpseclibReferences
https://github.com/phpseclib/phpseclib/commit/ffe48b6b1b1af6963327f0a5330e3aa004a194achttps://github.com/phpseclib/phpseclib/releases/tag/1.0.28https://github.com/phpseclib/phpseclib/releases/tag/2.0.53https://github.com/phpseclib/phpseclib/releases/tag/3.0.51https://github.com/phpseclib/phpseclib/security/advisories/GHSA-r854-jrxh-36qx