Authenticated code execution via REST deserialization bypass
Published May 21, 2026 · Updated May 21, 2026
Insecure deserialization in Concrete CMS 9.5.0 and earlier allows remote authenticated users to execute code through its REST API. The ExpressEntryList block controller accepts JSON-decoded Boolean true as _fromCIF, allowing serialized data into filterFields and later into unserialize(). An administrator able to add blocks must submit the payload, which executes when an administrator views or edits the block and grants server takeover.
Summary
What happened
Insecure deserialization in Concrete CMS 9.5.0 and earlier allows remote authenticated users to execute code through its REST API. The ExpressEntryList block controller accepts JSON-decoded Boolean true as _fromCIF, allowing serialized data into filterFields and later into unserialize(). An administrator able to add blocks must submit the payload, which executes when an administrator views or edits the block and grants server takeover.
The record
- CVE
- CVE-2026-8135
- Published
- May 21, 2026
- Updated
- May 21, 2026
- Vendor
- Concrete CMS
- Product
- Concrete CMS
- Classifications
- CWE-502, CAPEC-586, CAPEC-116, T1190
- Attack vector
- network
- Privileges
- admin
Timeline
How it unfolded
- May 21, 2026CVE publishedPublication date reported by the CVE source.
- May 21, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=5.0 <=9.5.0
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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