CVE-2026-34876
Out-of-Bounds Read in Mbed TLS CCM API Exposes Sensitive Data
Publication date: 2026-04-02
Last updated on: 2026-04-07
Assigner: MITRE
Description
Description
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| arm | mbed_tls | From 3.1.0 (inc) to 3.6.6 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-125 | The product reads data past the end, or before the beginning, of the intended buffer. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
CVE-2026-34876 is a vulnerability in Mbed TLS versions 3.x before 3.6.6 involving an out-of-bounds read in the function mbedtls_ccm_finish(). This occurs because the tag_len parameter is not properly validated against the size of the internal 16-byte authentication buffer during the multipart CCM API operation. As a result, attackers can read adjacent CCM context data by invoking the multipart CCM API with an oversized tag_len parameter.
Additionally, in Mbed TLS 4.x versions prior to the fix, the same missing validation exists internally, but the vulnerable function is not exposed via the public API.
This vulnerability allows attackers to bypass the integrity check of the final authentication tag in CCM mode, potentially accepting forged or tampered data without detection.
How can this vulnerability impact me? :
This vulnerability can impact you by allowing attackers to bypass the integrity verification of data processed using the CCM multipart API in affected Mbed TLS versions. This means that forged or tampered data could be accepted as valid, compromising the integrity and security of your data.
Exploitation requires that the application directly invokes the multipart CCM API with an oversized tag_len parameter, which could lead to unauthorized access to adjacent sensitive data in memory.
What immediate steps should I take to mitigate this vulnerability?
To mitigate this vulnerability, you should update Mbed TLS to version 3.6.6 or later, where the missing validation of the tag_len parameter in the multipart CCM API has been fixed.
If updating immediately is not possible, avoid using the multipart CCM API with untrusted or oversized tag_len parameters to prevent exploitation.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
The vulnerability in Mbed TLS allows attackers to bypass the integrity check of the CCM authentication tag, potentially leading to acceptance of forged or tampered data without detection. This compromises data integrity and security.
Since data integrity and security are critical requirements under common standards and regulations such as GDPR and HIPAA, this vulnerability could negatively impact compliance by exposing protected data to unauthorized modification or forgery.