CVE-2026-73857: Memory Corruption (CVSS 7.5)

Description

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.15 until 3.0.17, XML request body processing with SecParseXmlIntoArgs set to On or OnlyArgs can leave XMLNodes::parsing_ctx_arg uninitialized in the SAX end-element callback. A single crafted unauthenticated HTTP request can make a worker dereference the pointer, resulting in a constant-value write to an attacker-controlled address. The resulting memory corruption can terminate the worker and may disclose memory or redirect execution. Earlier 3.0.x releases and ModSecurity 2.x do not use the affected path. This issue is fixed in version 3.0.17.

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CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0040

Probability of exploitation

0.35%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-787 Out-of-bounds Write

CWE-824 CWE-824

References

Other References

https://github.com/owasp-modsecurity/ModSecurity/commit/e979a73e89d60cefdf42b41bb38bf1e456d7909f https://github.com/owasp-modsecurity/ModSecurity/releases/tag/v3.0.17 https://github.com/owasp-modsecurity/ModSecurity/security/advisories/GHSA-jx3r-phvx-2jmj

Frequently Asked Questions

What is CVE-2026-73857? +

ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. From 3.0.15 until 3.0.17, XML request body processing with SecParseXmlIntoArgs set to On or OnlyArgs can leave XMLNodes::parsing_ctx_arg uninitialized in the SAX end-element callback. A single crafted unauthenticated HTTP request can make a worker dereference the pointer, resulting in a constant-value write to an attacker-controlled address. The resulting memory corruption can terminate the worker and may disclose memory or redirect execution. Earlier 3.0.x releases and ModSecurity 2.x do not use the affected path. This issue is fixed in version 3.0.17. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-73857? +

CVE-2026-73857 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0040, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-73857? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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