PHP up to 8.4.20/8.5.5 out-of-bounds

Summaryinfo

A vulnerability was found in PHP up to 8.4.20/8.5.5. It has been declared as critical. This affects the function mb_convert_encoding/mb_detect_encoding/mb_convert_variables/mb_detect_order. Such manipulation leads to out-of-bounds. This vulnerability is referenced as CVE-2026-6104. It is possible to launch the attack remotely. No exploit is available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in PHP up to 8.4.20/8.5.5 and classified as critical. Affected by this issue is the function mb_convert_encoding/mb_detect_encoding/mb_convert_variables/mb_detect_order. The manipulation with an unknown input leads to a out-of-bounds vulnerability. Using CWE to declare the problem leads to CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-6104 since 04/11/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 07/03/2026).

The vulnerability scanner Nessus provides a plugin with the ID 313734 (Fedora 44 : php (2026-c66eaae759)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 8.4.21 or 8.5.6 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (313734) and CERT Bund (WID-SEC-2026-1433). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Affected

• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• Fedora Linux
• Ubuntu Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• RESF Rocky Linux
• Microsoft Azure Linux
• Open Source PHP
• Zend ZendPHP
• cPanel cPanel/WHM

Productinfo

Type

• Programming Language Software

Name

• PHP

Version

• 8.4.0
• 8.4.1
• 8.4.2
• 8.4.3
• 8.4.4
• 8.4.5
• 8.4.6
• 8.4.7
• 8.4.8
• 8.4.9
• 8.4.10
• 8.4.11
• 8.4.12
• 8.4.13
• 8.4.14
• 8.4.15
• 8.4.16
• 8.4.17
• 8.4.18
• 8.4.19
• 8.4.20
• 8.5.0
• 8.5.1
• 8.5.2
• 8.5.3
• 8.5.4
• 8.5.5

License

• open-source

Website

• Product: https://www.php.org/

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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