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CVE-2026-34876

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in...

7.5 HighFix available

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

0.41%Up 0.4 points since Apr 3, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
CVE-2026-34876
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-125
Updated
2026-11-02
EUVDEUVD-2026-18356 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
EUVD-2026-18356
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
GitHub AdvisoriesGHSA-jw9g-6hxw-4whq 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in...

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
GHSA-jw9g-6hxw-4whq
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-125
Updated
2026-11-02
NVD 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
CVE-2026-34876
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-125
Updated
2026-11-02
OSV 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
CVE-2026-34876
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2026-34876 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
DEBIAN-CVE-2026-34876
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2026-34876 7.5

An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vulnerability in mbedtls_ccm_finish() in library/ccm.c allows attackers to obtain adjacent CCM context data via invocation of the multipart CCM API with an oversized tag_len parameter. This is caused by missing validation of the tag_len parameter against the size of the internal 16-byte authentication buffer. The issue affects the public multipart CCM API in Mbed TLS 3.x, where mbedtls_ccm_finish() can be invoked directly by applications. In Mbed TLS 4.x versions prior to the fix, the same missing validation exists in the internal implementation; however, the function is not exposed as part of the public API. Exploitation requires application-level invocation of the multipart CCM API.

Record
UBUNTU-CVE-2026-34876
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVopenSUSE-SU-2026:10498-1 No score

libeverest-3.6.6-1.1 on GA media

These are all security issues fixed in the libeverest-3.6.6-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:10498-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
mbedtls
Debian:12
All versions, plus listed versions
2.28.3-12.28.4-12.28.5-12.28.6-12.28.7-1
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2.28.7-1.12.28.7-1.1~exp12.28.8-13.6.0-13.6.0-23.6.0-33.6.2-13.6.2-23.6.2-33.6.3-13.6.4-13.6.4-23.6.5-0.13.6.5-0.1~deb13u13.6.6-0.13.6.6-0.1~deb13u13.6.7-23.6.7-3
None known
mbedtls
Debian:13
before 3.6.6-0.1~deb13u1, plus listed versions
3.6.4-23.6.5-0.13.6.5-0.1~deb13u1
3.6.6-0.1~deb13u1
mbedtls
Debian:14
before 3.6.6-0.1, plus listed versions
3.6.4-23.6.5-0.13.6.5-0.1~deb13u13.6.6-0.1~deb13u1
3.6.6-0.1
mbedtls
Ubuntu:16.04:LTS
All versions, plus listed versions
2.1.2-12.2.0-12.2.1-12.2.1-22.2.1-2ubuntu0.12.2.1-2ubuntu0.22.2.1-2ubuntu0.3
None known
mbedtls
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
2.5.1-1ubuntu12.6.0-12.7.0-22.8.0-12.8.0-1ubuntu0.1~esm1
None known
mbedtls
Ubuntu:Pro:20.04:LTS
All versions, plus listed versions
2.16.2-12.16.3-12.16.4-1ubuntu22.16.4-1ubuntu2+esm1
None known
mbedtls
Ubuntu:Pro:22.04:LTS
All versions, plus listed versions
2.16.9-0.1ubuntu12.16.11-0.1ubuntu12.16.11-0.32.28.0-12.28.0-1build12.28.0-1ubuntu0.1~esm1
None known
mbedtls
Ubuntu:Pro:24.04:LTS
All versions, plus listed versions
2.28.3-12.28.6-1ubuntu12.28.7-1ubuntu12.28.7-1.1ubuntu12.28.8-12.28.8-1ubuntu0.1~esm1
None known
mbedtls
Ubuntu:25.10
All versions, plus listed versions
3.6.2-3ubuntu1
None known
mbedtls
Ubuntu:26.10
All versions, plus listed versions
3.6.5-0.1ubuntu23.6.6-0.1ubuntu13.6.7-3ubuntu1
None known
mbedtls
Ubuntu:26.04:LTS
All versions, plus listed versions
3.6.2-3ubuntu13.6.5-0.1ubuntu13.6.5-0.1ubuntu2
None known
mbedtls
openSUSE:Tumbleweed
From an advisory covering 10 CVEs
before 3.6.6-1.1
3.6.6-1.1

History

History
RecordedChangedSources
affected, facts
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-34876 is a high vulnerability (CVSS 7.5) in Trustedfirmware Mbed Tls, published April 2, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.41%, the 35th percentile. Fixed in mbedtls 3.6.6-0.1~deb13u1.

References

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