CVE-2026-91939: Insecure Deserialization (CVSS 9.8)

Description

Cotonti 1.0.0 Comments plugin passes the ci GET parameter to unserialize() without allowed_classes restriction, allowing unauthenticated attackers to instantiate arbitrary PHP classes with attacker-controlled properties. Attackers can exploit PHP object injection through crafted serialized payloads to trigger gadget chains and achieve database manipulation or code execution.

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CVSS v3.1 Score

9.8

CRITICAL

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

EPSS — Exploit Prediction

0.0059

Probability of exploitation

0.47%

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-502 Deserialization of Untrusted Data

References

Other References

https://github.com/Cotonti/Cotonti https://github.com/Cotonti/Cotonti/blob/1.0.0/plugins/comments/comments.setup.php https://github.com/Cotonti/Cotonti/blob/1.0.0/plugins/comments/controllers/actions/DisplayAction.php https://github.com/Cotonti/Cotonti/blob/1.0.0/plugins/comments/inc/CommentsWidget.php https://github.com/Cotonti/Cotonti/issues/1888 https://github.com/Cotonti/Cotonti/pull/1889 https://www.vulncheck.com/advisories/cotonti-1.0.0-comments-plugin-php-object-injection-via-ci-parameter https://github.com/Cotonti/Cotonti/issues/1888

Frequently Asked Questions

What is CVE-2026-91939? +

Cotonti 1.0.0 Comments plugin passes the ci GET parameter to unserialize() without allowed_classes restriction, allowing unauthenticated attackers to instantiate arbitrary PHP classes with attacker-controlled properties. Attackers can exploit PHP object injection through crafted serialized payloads to trigger gadget chains and achieve database manipulation or code execution. It has a CVSS v3.1 base score of 9.8 (CRITICAL).

How severe is CVE-2026-91939? +

CVE-2026-91939 has a CVSS v3.1 score of 9.8 out of 10, rated CRITICAL. This is a critical vulnerability that should be patched immediately. The EPSS score is 0.0059, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-91939? +

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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