CCM context disclosure via unchecked tag length
Published Apr 2, 2026 · Updated Apr 2, 2026
Out-of-bounds read in Mbed TLS 3.1.0 through 3.6.5 allows attackers to disclose adjacent CCM context memory via the multipart API. mbedtls_ccm_finish() passes a caller-supplied tag_len to memcpy against the 16-byte ctx->y buffer without validating its range or upper bound. Exploitation requires an application path that exposes the multipart CCM API with attacker-controlled parameters; the read can expose nonce, length, mode, or block-cipher context data but cannot modify memory or directly execute code.
Summary
What happened
Out-of-bounds read in Mbed TLS 3.1.0 through 3.6.5 allows attackers to disclose adjacent CCM context memory via the multipart API. mbedtls_ccm_finish() passes a caller-supplied tag_len to memcpy against the 16-byte ctx->y buffer without validating its range or upper bound. Exploitation requires an application path that exposes the multipart CCM API with attacker-controlled parameters; the read can expose nonce, length, mode, or block-cipher context data but cannot modify memory or directly execute code.
The record
- CVE
- CVE-2026-34876
- Published
- Apr 2, 2026
- Updated
- Apr 2, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-125
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 2, 2026CVE publishedPublication date reported by the CVE source.
- Apr 2, 2026Record updatedLatest update available in the CVE record.
Exploitability
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Attacks
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