CVE-2026-6104

Critical · CVSS 9.1

PHP mbstring extension — Out-of-bounds read via NUL byte in encoding name (CWE-125)

CVSS: 9.1; nvd
EPSS: —
KEV: No
Class: other; CWE-125, 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.

Search profile — drives PoC discovery

Symbols mb_convert_encodingmb_detect_encodingmb_convert_variablesmb_detect_orderstrncasecmpmbstring.detect_ordermbstring.http_outputphp_mbstringmbstring

Keywords CVE-2026-6104PHP mbstring NUL byte out-of-bounds readmb_convert_encoding NUL bytembstring encoding name embedded nullPHP 8.4 mbstring OOB readPHP 8.5 mbstring information disclosurestrncasecmp NUL byte mbstringGHSA-74r9-qxhc-fx53

Versions: 8.4.* before 8.4.21, 8.5.* before 8.5.6

References

Status: enriched · ingested 2026-06-30T06:00:22.000Z · profiled 2026-07-01T18:30:14.000Z