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Fencer Vulns
high 7.2

CVE-2021-36766 json

Concrete5 through 8.5.5 deserializes Untrusted Data.

published 2021-07-27 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-23354

cvss
7.2
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
3.7%
EPSS 3.7% chance of exploitation in 30 days, percentile 89%
public exploits
0
none known

Summary

Concrete5 through 8.5.5 deserializes Untrusted Data. The vulnerable code is located within the controllers/single_page/dashboard/system/environment/logging.php Logging::update_logging() method. User input passed through the logFile request parameter is not properly sanitized before being used in a call to the file_exists() PHP function. This can be exploited by malicious users to inject arbitrary PHP objects into the application scope (PHP Object Injection via phar:// stream wrapper), allowing them to carry out a variety of attacks, such as executing arbitrary PHP code.

Patch / fix

  • concretecms concrete_cms 8.5.6

Exploit prediction

3.68% chance of exploitation in the next 30 days, higher than 89% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • seclists.org http://seclists.org/fulldisclosure/2021/Jul/36 referenced PoC, tagged "exploit" by a source, unverified
  • packetstormsecurity.com http://packetstormsecurity.com/files/163564/Concrete5-8.5.5-Phar-Deserialization.html referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 7.2 CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.5 AV:N/AC:L/Au:S/C:P/I:P/A:P

Classification

Weakness
  • CWE-502 Deserialization of Untrusted Data

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.