phpseclib has a variable-time HMAC comparison in SSH2::get_binary_packet() using != instead of hash_equals()

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Summary

CVECVE-2026-40194
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-04-10 21:16:27 UTC
Updated2026-04-10 21:16:27 UTC
Descriptionphpseclib 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.

Risk And Classification

Primary CVSS: v3.1 3.7 LOW from [email protected]

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Problem Types: CWE-208 | CWE-208 CWE-208: Observable Timing Discrepancy

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
3.1CNADECLARED3.7LOWCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Phpseclib Phpseclib affected < 1.0.28 Not specified
CNA Phpseclib Phpseclib affected >= 2.0.0, < 2.0.53 Not specified
CNA Phpseclib Phpseclib affected >= 3.0.0, < 3.0.51 Not specified

References

ReferenceSourceLinkTags
github.com/phpseclib/phpseclib/releases/tag/3.0.51 [email protected] github.com
github.com/phpseclib/phpseclib/security/advisories/GHSA-r854-jrxh-36qx [email protected] github.com
github.com/phpseclib/phpseclib/releases/tag/1.0.28 [email protected] github.com
github.com/phpseclib/phpseclib/commit/ffe48b6b1b1af6963327f0a5330e3aa004... [email protected] github.com
github.com/phpseclib/phpseclib/releases/tag/2.0.53 [email protected] github.com
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