GHSA-pv2v-6w2v-97x6 CVE-2026-8135
Concrete CMS Vulnerable to Deserialization of Untrusted Data
- Severity
- 0.0 / 10
- High · CVSS 4.0
- Exploit chance (EPSS)
- 0.47%
- Chance of exploitation in the next 30 days. Higher than 40.71% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-502 Deserialization of Untrusted Data
- Fix
9.5.1- Upgrade concrete5/concrete5 to this version or later
Description
Concrete CMS 9.5.0 and below is vulnerable to Remote Code Execution due to insecure deserialization occurring in the ExpressEntryList block controller. An rogue administrator with privileges to add blocks to an area can bypass the intended protection mechanism (_fromCIF === true), which normally restricts malicious inputs over form POST requests, by leveraging the REST API functionality. Because the REST API parses requests using json_decode(), the string "true" is evaluated as a strict PHP Boolean(true). This bypass allows the attacker to inject a malicious serialized payload into the block's filterFields database column. The payload will subsequently be executed when the block's data is viewed or edited by an administrator leading to complete server takeover (RCE). Concrete CMS thanks Nguyễn Văn Thiện https://github.com/Thien225409 for reporting this issue.
Affected versions
Packagist
| Package | Vulnerable | Fixed in |
|---|---|---|
| concrete5/concrete5 | < 9.5.1 |
9.5.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
concrete5/concrete5 Packagist → 9.5.1
- composer
composer require concrete5/concrete5:^9.5.1
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- Attack vector
- Network
- Attack complexity
- High
- Attack requirements
- Present
- Privileges required
- High
- User interaction
- None
- Confidentiality (vulnerable system)
- High
- Integrity (vulnerable system)
- High
- Availability (vulnerable system)
- High
- Confidentiality (subsequent systems)
- High
- Integrity (subsequent systems)
- High
- Availability (subsequent systems)
- High
CVSS 3.1 7.2
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
Weakness
CWE-502: Deserialization of Untrusted Data
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
How to prevent it
- Architecture and Design, Implementation: If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
- Implementation: When deserializing data, populate a new object rather than just deserializing. The result is that the data flows through safe input validation and that the functions are safe.
- Implementation: Explicitly define a final object() to prevent deserialization.
- Architecture and Design, Implementation: Make fields transient to protect them from deserialization. An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.
- Implementation: Avoid having unnecessary types or gadgets (a sequence of instances and method invocations that can self-execute during the deserialization process, often found in libraries) available that can be leveraged for malicious ends. This limits the potential for unintended or unauthorized types and gadgets to be leveraged by the attacker. Add only acceptable classes to an allowlist. Note: new gadgets are constantly being discovered, so this alone is not a sufficient mitigation.
- Architecture and Design, Implementation: Employ cryptography of the data or code for protection. However, it's important to note that it would still be client-side security. This is risky because if the client is compromised then the security implemented on the client (the cryptography) can be bypassed.
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
References
Advisories
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-g82f-9pw7-773w Concrete CMS: PHP Object Injection via unserialize() calls | High | Also affects concrete5/concrete5 |
| GHSA-52pr-7vmf-2w7x Concrete CMS is vulnerable to PHP Object Injection via unserialize() calls in the Workflow, Form block, and File/Set components | High | Also affects concrete5/concrete5 |
| GHSA-q9fm-mpg8-8jqm Concrete CMS is vulnerable to Stored XSS via page name in the Atomik theme | Medium | Also affects concrete5/concrete5 |
| GHSA-jqvq-gv67-3567 Concrete CMS is vulnerable to IDOR + wrong-authorization-level in the Express association Reorder dialog | Medium | Also affects concrete5/concrete5 |
| GHSA-xjg6-5v39-v7fc Concrete CMS is vulnerable to CSRF via Backend\File::approveVersion | Medium | Also affects concrete5/concrete5 |
| GHSA-44q4-354f-c826 Concrete CMS is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/backend/file approveVersion() | Medium | Also affects concrete5/concrete5 |
| GHSA-6qjh-p324-694f Concrete CMS is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/backend/file rescanMultiple() | High | Also affects concrete5/concrete5 |
| GHSA-6fxm-r8p3-mx5c Concrete CMS is vulnerable to Cross Site Request Forgery (CSRF) at concrete/controllers/backend/file rescan() | High | Also affects concrete5/concrete5 |
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