critical CVSS 9.9

CVE-2026-23836·PHP vulnerability

HotCRP is conference review software. A problem introduced in April 2024 in version 3.1 led to inadequately sanitized code generation for HotCRP formulas which allowed users to trigger the execution of arbitrary PHP code. The problem is patched in release version 3.2.

Severity
critical
Software
PHP
Fixed in
3.2
Published
2026-01-19

Affected versions

From: 3.0

Until: 3.2

Fixed in: 3.2

How to fix this CVE

Update PHP to version 3.2 or later to remediate CVE-2026-23836, which allows authenticated users to execute arbitrary PHP code through inadequately sanitized formula generation in HotCRP. Organizations running HotCRP versions 3.0 through 3.1 should prioritize this update immediately due to the critical severity rating. Verify the update installation and restart PHP-FPM or your web server to ensure the patched code is loaded.

sudo dnf update php

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST /api/formula|GET /formula.php with malicious PHP code payloads in 'formula' or 'code' parameters; look for eval(), system(), exec(), passthru() function calls in application logs following formula submission requests

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement WAF rules to block HTTP requests containing PHP code syntax (<?php, eval, system, exec, passthru, shell_exec) in formula-related parameters; restrict formula submission endpoints to authenticated users only and rate-limit formula processing requests to detect brute-force injection attempts

How to check if you are affected

  1. Run 'php -v' to determine the currently installed PHP version and verify it is 3.2 or later
  2. If using HotCRP, check the application version in the web interface (typically in admin settings or footer) to confirm it is 3.2+
  3. Search application logs for formula-related function calls or eval() execution attempts: grep -i 'formula\|eval' /var/log/php-fpm.log /var/log/apache2/error.log /var/log/nginx/error.log
  4. Verify patch installation by checking git commit history if deployed from source: git log --oneline | grep -i 'formula\|sanitiz' or examine /usr/share/php for file modification timestamps matching the update date

FAQ

What is CVE-2026-23836?

CVE-2026-23836 is a critical PHP code injection vulnerability in HotCRP's formula processing engine that was introduced in April 2024. The flaw allows authenticated users with formula-writing privileges to inject and execute arbitrary PHP code by bypassing input sanitization controls.

Is CVE-2026-23836 being actively exploited?

No, CVE-2026-23836 is not listed on CISA's Known Exploited Vulnerabilities catalog and no public exploits are currently available. However, the critical CVSS score and authentication-only requirement make it a priority target for insider threats.

What versions of PHP are affected by CVE-2026-23836?

HotCRP versions 3.0, 3.1, and early releases of 3.2 (prior to the security patch commits) are vulnerable. The vulnerability was fixed in HotCRP 3.2 with security patches released on GitHub.

How do I check if my server is vulnerable to CVE-2026-23836?

Run 'php -v' to check your PHP version, then verify your HotCRP installation version through the admin panel or by checking the version.php file. If running HotCRP 3.0 or 3.1, your system is vulnerable and requires immediate patching.

Does Defensia detect CVE-2026-23836?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If PHP or HotCRP is installed on a monitored server, CVE-2026-23836 will appear in your dashboard with remediation steps.

Related PHP CVEs

CVE-2025-46348CVSS 10YesWiki is a wiki system written in PHP. Prior to version 4.5.4, the request to commence a site backup can be performed and downloaded without authentication. The archives are created with a predictable filename, so a malicious user could create and download an archive without being authenticated. This could result in a malicious attacker making numerous requests to create archives and fill up the file system, or by downloading the archive which contains sensitive site information. This issue has been patched in version 4.5.4.
CVE-2025-25174CVSS 10Improper Control of Filename for Include/Require Statement in PHP Program ('PHP Remote File Inclusion') vulnerability in beeteam368 BeeTeam368 Extensions beeteam368-extensions allows PHP Local File Inclusion.This issue affects BeeTeam368 Extensions: from n/a through <= 1.9.4.
CVE-2026-39337CVSS 10ChurchCRM is an open-source church management system. Prior to 7.1.0, critical pre-authentication remote code execution vulnerability in ChurchCRM's setup wizard allows unauthenticated attackers to inject arbitrary PHP code during the initial installation process, leading to complete server compromise. The "$dbPassword" variable is not sanitized. This vulnerability exists due to an incomplete fix for CVE-2025-62521. This vulnerability is fixed in 7.1.0.
CVE-2025-62521CVSS 10ChurchCRM is an open-source church management system. Prior to version 5.21.0, a pre-authentication remote code execution vulnerability in ChurchCRM's setup wizard allows unauthenticated attackers to inject arbitrary PHP code during the initial installation process, leading to complete server compromise. The vulnerability exists in `setup/routes/setup.php` where user input from the setup form is directly concatenated into a PHP configuration template without any validation or sanitization. Any parameter in the setup form can be used to inject PHP code that gets written to `Include/Config.php`, which is then executed on every page load. This is more severe than typical authenticated RCE vulnerabilities because it requires no credentials and affects the installation process that administrators must complete. Version 5.21.0 patches the issue.
CVE-2025-47916CVSS 10Invision Community 5.0.0 before 5.0.7 allows remote code execution via crafted template strings to themeeditor.php. The issue lies within the themeeditor controller (file: /applications/core/modules/front/system/themeeditor.php), where a protected method named customCss can be invoked by unauthenticated users. This method passes the value of the content parameter to the Theme::makeProcessFunction() method; hence it is evaluated by the template engine. Accordingly, this can be exploited by unauthenticated attackers to inject and execute arbitrary PHP code by providing crafted template strings.

References

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2026-23836. Free for 1 server.

Get started free