Cotonti Comments CreateAction.php prepareComeBack ci/cb deserialization

Summaryinfo

A vulnerability described as critical has been identified in Cotonti. The affected element is the function prepareComeBack of the file plugins/comments/controllers/actions/CreateAction.php of the component Comments. Such manipulation of the argument ci/cb leads to deserialization. This vulnerability is documented as CVE-2026-71294. The attack can be executed remotely. There is not any exploit available.

Detailsinfo

A vulnerability was found in Cotonti (unknown version). It has been rated as critical. Affected by this issue is the function prepareComeBack of the file plugins/comments/controllers/actions/CreateAction.php of the component Comments. The manipulation of the argument ci/cb with an unknown input leads to a deserialization vulnerability. Using CWE to declare the problem leads to CWE-502. The product deserializes untrusted data without sufficiently verifying that the resulting data will be valid. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Cotonti CMS's Comments plugin deserializes user-supplied data without restricting the classes that may be instantiated. In plugins/comments/controllers/actions/CreateAction.php, a `ci` POST parameter obtained via `cot_import('ci', 'P', 'TXT')` (trim-only sanitization) is passed to `unserialize(base64_decode($ci))` with no `allowed_classes` restriction, reachable by any member with write access to comments (the default `Auth_members => 'RW'` setting in plugins/comments/comments.setup.php). In plugins/comments/controllers/actions/EditAction.php, a `cb` parameter is similarly deserialized via `unserialize(base64_decode($this->comeback))` in prepareComeBack(), reachable by any member editing their own comment. Because unserialize() is called without allowed_classes, an attacker can construct a serialized PHP object of any class loaded by Cotonti (a PHP Object Injection primitive). This was demonstrated in practice using Cotonti's own MySQL_cache class: a crafted serialized MySQL_cache object, once deserialized and later garbage-collected, triggers its __destruct()->flush() chain, causing an attacker-controlled INSERT INTO cot_cache with attacker-chosen row values — confirming genuine POP-chain exploitation, with further impact (including potential RCE) contingent on other gadget chains available in a given Cotonti installation's loaded classes. A third sink in DeleteAction.php contains the identical unserialize() pattern but is gated behind an admin-only authorization check and is not reachable by ordinary members.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-71294 since 08/05/2026. The exploitation is known to be easy. The attack may be launched remotely. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/05/2026).

By approaching the search of inurl:plugins/comments/controllers/actions/CreateAction.php it is possible to find vulnerable targets with Google Hacking.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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• Cotonti

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• 🔒

CPE 2.2info

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