medium CVSS 6.5

CVE-2026-7259·PHP vulnerability

In PHP versions 8.2.* before 8.2.31, 8.3.* before 8.3.31, 8.4.* before 8.4.21, and 8.5.* before 8.5.6, a mismatch between encoding lists in Oniguruma and mbfl leads to  a NULL pointer dereference, resulting in a segmentation fault and denial of service. The vulnerability is exploitable when user-controlled input can influence the encoding passed to mb_regex_encoding().

Severity
medium
Software
PHP
Fixed in
8.5.6
Published
2026-05-10

Affected versions

From: 8.5.0

Until: 8.5.6

Fixed in: 8.5.6

How to fix this CVE

Update PHP to version 8.5.6 or later to resolve a NULL pointer dereference vulnerability in the multibyte string regex functions. This vulnerability can cause application crashes when processing specially crafted input through mb_regex_encoding(). Apply the security patch immediately to restore service stability and prevent denial-of-service conditions.

sudo dnf update php

Defensia detects this vulnerability

How to check if you are affected

  1. Check installed PHP version: php -v | grep 'PHP 8'
  2. Verify if mb_regex_encoding() is used in your application: grep -r 'mb_regex_encoding' /var/www/html
  3. Search application logs for segmentation faults: grep -i 'segmentation fault\|segfault\|signal 11' /var/log/apache2/error.log /var/log/nginx/error.log /var/log/php-fpm.log
  4. Confirm patch installation: php -v should show 8.5.6 or later

FAQ

What is CVE-2026-7259?

CVE-2026-7259 is a denial-of-service vulnerability in PHP's multibyte regex functions caused by an encoding mismatch between the Oniguruma and mbfl libraries. When user input controls the encoding parameter in mb_regex_encoding(), a NULL pointer dereference triggers a segmentation fault and crashes the PHP process.

Is CVE-2026-7259 being actively exploited?

No, CVE-2026-7259 is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available. However, the attack surface is low-complexity and requires only network access, making proactive patching essential.

What versions of PHP are affected by CVE-2026-7259?

PHP 8.2.0 through 8.2.30, 8.3.0 through 8.3.30, 8.4.0 through 8.4.20, and 8.5.0 through 8.5.5 are affected. PHP 8.5.6 and later versions include the fix.

How do I check if my server is vulnerable to CVE-2026-7259?

Run php -v and compare your version against the affected ranges. If you are on 8.5.x and the version is below 8.5.6, your server is vulnerable.

Does Defensia detect CVE-2026-7259?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP is installed on a monitored server, CVE-2026-7259 will appear in your dashboard with remediation steps.

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References

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