CVE & CISA-KEV Catalog

CVE-2026-40194

LOW
3.7
CVSS v3
NVD

Description

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.

CWE-208

How to fix

Remediation Available
php-phpseclibDebian
Fixed in:2.0.30-2+deb11u3CVE-2026-40194
Fixed in:2.0.42-1+deb12u4CVE-2026-40194
Fixed in:2.0.48-3+deb13u2CVE-2026-40194
Fixed in:2.0.53-1CVE-2026-40194

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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork
Attack ComplexityHigh
Privileges RequiredNone
User InteractionNone
ScopeUnchanged

Impact

ConfidentialityLow
IntegrityNone
AvailabilityNone

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

Exploit Intelligence

0.36%probability of exploitation in 30 days
29thpercentile

Low risk: more likely to be exploited than 29% of all known CVEs.

References

Vendor Advisory1

Related Vulnerabilities

Other CWE-208 vulnerabilities, ordered by exploit likelihood. View all

CVESeverityCVSSEPSSExploitedFix
CVE-2019-9494Medium5.93.9%-Fix
CVE-2019-16782Medium6.33.7%-Fix
CVE-2025-53940Unscored-2.6%--
CVE-2020-1926Medium5.92.5%-Fix
CVE-2021-43298Critical9.82.3%-Fix
CVE-2024-29995High8.11.5%-Fix

Common questions

How do I fix CVE-2026-40194?

Upgrade php-phpseclib on debian 11 to 2.0.30-2+deb11u3 or later.

Is CVE-2026-40194 being actively exploited?

Not that we know of. CVE-2026-40194 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.36% is the estimated probability that it will be exploited in the next 30 days. That is higher than 29% of all scored CVEs.

How severe is CVE-2026-40194?

CVE-2026-40194 has a CVSS v3 base score of 3.7, rated low. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-40194 affect?

Published advisories record a fix for php-phpseclib (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-05-08.