CVE-2026-6104
NUL byte in mbstring encoding leads to out-of-bounds read
| Publication Date | 2026-05-10 |
|---|---|
| Severity | Moderate |
| Type | Information Disclosure |
| Affected PHP Versions |
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| Fixed Product Versions |
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CVE Details
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.
Recommendations
If using user-supplied encoding names with mbstring functions, ensure you validate them against known-good encodings, preferably using an allow-list.
When possible, update to a patched version of PHP.