phpseclib is a PHP secure communications library. 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.
Attack Parameters
Attack Vector
Network
Can be exploited remotely
Attack Complexity
High
Difficult to exploit
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed
Impact Assessment
Confidentiality
Low
Partial data leak
Integrity
None
No data modification
Availability
None
No disruption
CVSS Vector v3.1
Weakness Type (CWE)
References 5
https://github.com/phpseclib/phpseclib/commit/ffe48b6b1b1af6963327f0a5330e3aa00…
security-advisories@github.com
https://github.com/phpseclib/phpseclib/releases/tag/1.0.28
security-advisories@github.com
https://github.com/phpseclib/phpseclib/releases/tag/2.0.53
security-advisories@github.com
https://github.com/phpseclib/phpseclib/releases/tag/3.0.51
security-advisories@github.com
https://github.com/phpseclib/phpseclib/security/advisories/GHSA-r854-jrxh-36qx
security-advisories@github.com