CVE-2026-6104

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.

Score

CVSS 3.1 9.1 Critical

Status

Modified - security@php.net

Published

2026-05-10

Last modified

2026-07-15

Weaknesses

CWE-125

Affected products

• Php (Php)
• Php (Php Group)
• Enterprise Linux (Redhat)
• Hummingbird (Redhat)

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