What is the CVSS score of CVE-2026-40194?

CVE-2026-40194 has a CVSS 3.1 base score of 3.7 (Low). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N. EPSS exploitation probability: 0.0%.

Is there a patch available for CVE-2026-40194?

Yes, a patch is available for CVE-2026-40194. Update the affected software to the latest version immediately.

PHP CVE-2026-40194

EUVD-2026-21597 LOW

Observable Timing Discrepancy (CWE-208)

2026-04-10 GitHub_M

GHSA-r854-jrxh-36qx

PHP Information Disclosure

3.7

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

3.7 LOW

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

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

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

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Lifecycle Timeline

Patch released

Apr 11, 2026 - 02:30 nvd

Patch available

EUVD ID Assigned

Apr 10, 2026 - 21:00 euvd

EUVD-2026-21597

Analysis Generated

Apr 10, 2026 - 21:00 vuln.today

CVE Published

Apr 10, 2026 - 20:24 nvd

LOW 3.7

DescriptionGitHub Advisory

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.

AnalysisAI

phpseclib's SSH2 packet authentication uses PHP's non-constant-time != operator to compare HMACs, enabling timing-based information disclosure attacks on SSH sessions. The vulnerability affects phpseclib versions prior to 1.0.28, 2.0.53, and 3.0.51. An unauthenticated remote attacker can exploit variable-time comparison behavior to infer valid HMAC values through precise timing measurements, potentially compromising the confidentiality of SSH communications. No public exploit code or active exploitation has been confirmed, but this is a cryptographic timing vulnerability with proven scalability via benchmarking.

Technical ContextAI

phpseclib implements SSH protocol functionality via the Net\SSH2 class, which validates packet integrity using HMAC-based authentication codes. The vulnerability resides in the get_binary_packet() method, which employs PHP's != operator for HMAC comparison. In PHP, the != operator on binary strings of equal length internally uses the C memcmp() function, which performs byte-by-byte comparison and exits immediately upon finding the first differing byte. This short-circuit behavior creates a measurable timing side-channel (CWE-208: Observable Timing Discrepancy): valid HMACs require memcmp() to compare all bytes before returning false, while invalid HMACs with differing early bytes return faster. By measuring response latency across many SSH packets with systematically varied HMACs, an attacker can narrow the valid HMAC byte-by-byte, reducing computational complexity from 2^(HMAC_length) to roughly 256 * HMAC_length attempts. The affected CPE (cpe:2.3:a:phpseclib:phpseclib) spans all installations prior to the patched releases.

RemediationAI

Vendor-released patches are available: upgrade to phpseclib 1.0.28 or later, 2.0.53 or later, or 3.0.51 or later, depending on the current major version in use. Apply the patch immediately if phpseclib is used in SSH connections across untrusted networks or where attackers may control network latency measurements. Workarounds are not practical for this cryptographic issue; patching is required. Refer to the official security advisory at https://github.com/phpseclib/phpseclib/security/advisories/GHSA-r854-jrxh-36qx and verify the patched release via https://github.com/phpseclib/phpseclib/releases (tags 1.0.28, 2.0.53, and 3.0.51). The underlying fix (commit ffe48b6b1b1af6963327f0a5330e3aa004a194ac) replaces the != operator with hash_equals(), a constant-time comparison function.