critical CVSS 9.8

CVE-2026-17544·PHP vulnerability

Attacker-provided inputs to bccomp() could lead to an out-of-bounds write with stack and heap corruption in PHP versions from 8.4.* before 8.4.24 and from 8.5.* before 8.5.9.

Severity
critical
Software
PHP
Fixed in
8.5.9
Published
2026-07-30

Affected versions

From: 8.5.0

Until: 8.5.9

Fixed in: 8.5.9

How to fix this CVE

Upgrade PHP to version 8.5.9 or later immediately, as earlier 8.5.x versions contain a critical memory corruption flaw in the bccomp() function that can be triggered by malicious input. This vulnerability allows remote attackers to corrupt stack and heap memory without authentication, potentially leading to arbitrary code execution. Verify the upgrade completion and test bccomp() functionality in your applications before returning to production.

sudo dnf update php

Defensia detects this vulnerability

How to check if you are affected

  1. Step 1: Run `php -v` to display the installed PHP version and confirm if it falls within 8.5.0 to 8.5.8
  2. Step 2: Check if bccomp() is used in your application by searching source code with `grep -r 'bccomp' /var/www /home /opt --include='*.php'`
  3. Step 3: Review PHP error logs at `/var/log/php-errors.log` or `/var/log/apache2/error.log` for segmentation faults or memory corruption warnings coinciding with bccomp() calls
  4. Step 4: After patching, run `php -v` again and confirm version is 8.5.9 or higher, then execute a test script calling bccomp() to verify normal operation

FAQ

What is CVE-2026-17544?

This is a critical memory safety vulnerability in PHP's bccomp() function that processes untrusted numerical comparison inputs. Attackers can craft specially-formatted input to trigger an out-of-bounds write operation, corrupting both stack and heap memory regions and potentially executing arbitrary code.

Is CVE-2026-17544 being actively exploited?

No, this vulnerability is not currently listed on the CISA Known Exploited Vulnerabilities catalog and no public exploits are known to exist at this time. However, given the critical severity, patches should still be applied proactively.

What versions of PHP are affected by CVE-2026-17544?

PHP 8.5.0 through 8.5.8 are vulnerable. Versions 8.4.x prior to 8.4.24 may also be affected according to the advisory. PHP 8.5.9 and later versions contain the fix.

How do I check if my server is vulnerable to CVE-2026-17544?

Execute `php -v` and check if the reported version is between 8.5.0 and 8.5.8 inclusive. If so, your installation is vulnerable and requires immediate patching to 8.5.9 or later.

Does Defensia detect CVE-2026-17544?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP is installed on a monitored server, CVE-2026-17544 will appear in your dashboard with remediation steps.

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References

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