What’s Vulnerable › Vulnerabilities

CVE-2026-6104: Global buffer over-read in mb_convert_encoding() with attacker-supplied encoding

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-10 · updated 2026-07-24
• Weakness: CWE-125

Description

In PHP versions 8.4.* before 8.4.21 and 8.5.* before 8.5.6, when an encoding name containing an embedded NUL byte is passed to mb_convert_encoding() or related mbstring functions, the code incorrectly assumes that when strncasecmp() returns 0 it means the strings have the same length. This can lead to out-of-bounds read of global memory, potentially causing a crash or information disclosure or crash. Affected functions include mb_convert_encoding(), mb_detect_encoding(), mb_convert_variables(), and mb_detect_order(), as well as the mbstring.detect_order and mbstring.http_output INI settings.

Affected products

• PHP: from 8.4.0 before 8.4.21; from 8.5.0 before 8.5.6 — fixed in 8.4.21, 8.5.6

How to fix

Upgrade to a fixed version: PHP 8.4.21, 8.5.6. Check the vendor advisory for mitigations.

References

• https://github.com/php/php-src/security/advisories/GHSA-74r9-qxhc-fx53
• https://access.redhat.com/errata/RHSA-2026:22649
• https://access.redhat.com/security/cve/CVE-2026-6104
• https://bugzilla.redhat.com/show_bug.cgi?id=2468573
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-6104.json

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