GHSA-RM37-V7MC-6795
Vulnerability from github – Published: 2026-08-05 15:32 – Updated: 2026-08-10 12:31Cotonti 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.
{
"affected": [],
"aliases": [
"CVE-2026-71294"
],
"database_specific": {
"cwe_ids": [
"CWE-502"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-08-05T13:24:54Z",
"severity": "HIGH"
},
"details": "Cotonti CMS\u0027s 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(\u0027ci\u0027, \u0027P\u0027, \u0027TXT\u0027)` (trim-only sanitization) is passed to `unserialize(base64_decode($ci))` with no `allowed_classes` restriction, reachable by any member with write access to comments (the default `Auth_members =\u003e \u0027RW\u0027` setting in plugins/comments/comments.setup.php). In plugins/comments/controllers/actions/EditAction.php, a `cb` parameter is similarly deserialized via `unserialize(base64_decode($this-\u003ecomeback))` 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\u0027s own MySQL_cache class: a crafted serialized MySQL_cache object, once deserialized and later garbage-collected, triggers its __destruct()-\u003eflush() chain, causing an attacker-controlled INSERT INTO cot_cache with attacker-chosen row values \u2014 confirming genuine POP-chain exploitation, with further impact (including potential RCE) contingent on other gadget chains available in a given Cotonti installation\u0027s 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.",
"id": "GHSA-rm37-v7mc-6795",
"modified": "2026-08-10T12:31:50Z",
"published": "2026-08-05T15:32:22Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-71294"
},
{
"type": "WEB",
"url": "https://github.com/Cotonti/Cotonti"
},
{
"type": "WEB",
"url": "https://github.com/Cotonti/Cotonti/blob/master/plugins/comments/controllers/actions/CreateAction.php"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:L",
"type": "CVSS_V3"
}
]
}
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