ubuntu-cve-2026-34876
Vulnerability from osv_ubuntu
Published
2026-04-02 16:16
Modified
2026-05-20 15:27
Summary
Details
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.
Severity
7.5 (High)
N/A (UNKNOWN)
References
{
"affected": [
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto0",
"binary_version": "2.2.1-2ubuntu0.3"
},
{
"binary_name": "libmbedtls10",
"binary_version": "2.2.1-2ubuntu0.3"
},
{
"binary_name": "libmbedx509-0",
"binary_version": "2.2.1-2ubuntu0.3"
}
]
},
"package": {
"ecosystem": "Ubuntu:16.04:LTS",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@2.2.1-2ubuntu0.3?arch=source\u0026distro=xenial"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.1.2-1",
"2.2.0-1",
"2.2.1-1",
"2.2.1-2",
"2.2.1-2ubuntu0.1",
"2.2.1-2ubuntu0.2",
"2.2.1-2ubuntu0.3"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto1",
"binary_version": "2.8.0-1ubuntu0.1~esm1"
},
{
"binary_name": "libmbedtls10",
"binary_version": "2.8.0-1ubuntu0.1~esm1"
},
{
"binary_name": "libmbedx509-0",
"binary_version": "2.8.0-1ubuntu0.1~esm1"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:18.04:LTS",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@2.8.0-1ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/bionic"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.5.1-1ubuntu1",
"2.6.0-1",
"2.7.0-2",
"2.8.0-1",
"2.8.0-1ubuntu0.1~esm1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto3",
"binary_version": "2.16.4-1ubuntu2+esm1"
},
{
"binary_name": "libmbedtls12",
"binary_version": "2.16.4-1ubuntu2+esm1"
},
{
"binary_name": "libmbedx509-0",
"binary_version": "2.16.4-1ubuntu2+esm1"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:20.04:LTS",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@2.16.4-1ubuntu2+esm1?arch=source\u0026distro=esm-apps/focal"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.16.2-1",
"2.16.3-1",
"2.16.4-1ubuntu2",
"2.16.4-1ubuntu2+esm1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto7",
"binary_version": "2.28.0-1ubuntu0.1~esm1"
},
{
"binary_name": "libmbedtls14",
"binary_version": "2.28.0-1ubuntu0.1~esm1"
},
{
"binary_name": "libmbedx509-1",
"binary_version": "2.28.0-1ubuntu0.1~esm1"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:22.04:LTS",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@2.28.0-1ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/jammy"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.16.9-0.1ubuntu1",
"2.16.11-0.1ubuntu1",
"2.16.11-0.3",
"2.28.0-1",
"2.28.0-1build1",
"2.28.0-1ubuntu0.1~esm1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto7t64",
"binary_version": "2.28.8-1ubuntu0.1~esm1"
},
{
"binary_name": "libmbedtls14t64",
"binary_version": "2.28.8-1ubuntu0.1~esm1"
},
{
"binary_name": "libmbedx509-1t64",
"binary_version": "2.28.8-1ubuntu0.1~esm1"
}
]
},
"package": {
"ecosystem": "Ubuntu:Pro:24.04:LTS",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@2.28.8-1ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/noble"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"2.28.3-1",
"2.28.6-1ubuntu1",
"2.28.7-1ubuntu1",
"2.28.7-1.1ubuntu1",
"2.28.8-1",
"2.28.8-1ubuntu0.1~esm1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto16",
"binary_version": "3.6.2-3ubuntu1"
},
{
"binary_name": "libmbedtls21",
"binary_version": "3.6.2-3ubuntu1"
},
{
"binary_name": "libmbedx509-7",
"binary_version": "3.6.2-3ubuntu1"
}
]
},
"package": {
"ecosystem": "Ubuntu:25.10",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@3.6.2-3ubuntu1?arch=source\u0026distro=questing"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"3.6.2-3ubuntu1"
]
},
{
"ecosystem_specific": {
"binaries": [
{
"binary_name": "libmbedcrypto16",
"binary_version": "3.6.5-0.1ubuntu2"
},
{
"binary_name": "libmbedtls21",
"binary_version": "3.6.5-0.1ubuntu2"
},
{
"binary_name": "libmbedx509-7",
"binary_version": "3.6.5-0.1ubuntu2"
}
]
},
"package": {
"ecosystem": "Ubuntu:26.04:LTS",
"name": "mbedtls",
"purl": "pkg:deb/ubuntu/mbedtls@3.6.5-0.1ubuntu2?arch=source\u0026distro=resolute"
},
"ranges": [
{
"events": [
{
"introduced": "0"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"3.6.2-3ubuntu1",
"3.6.5-0.1ubuntu1",
"3.6.5-0.1ubuntu2"
]
}
],
"aliases": [],
"details": "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.",
"id": "UBUNTU-CVE-2026-34876",
"modified": "2026-05-20T15:27:24Z",
"published": "2026-04-02T16:16:00Z",
"references": [
{
"type": "REPORT",
"url": "https://ubuntu.com/security/CVE-2026-34876"
},
{
"type": "REPORT",
"url": "https://www.cve.org/CVERecord?id=CVE-2026-34876"
},
{
"type": "REPORT",
"url": "https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/"
}
],
"related": [],
"schema_version": "1.7.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N",
"type": "CVSS_V3"
},
{
"score": "medium",
"type": "Ubuntu"
}
],
"upstream": [
"CVE-2026-34876"
]
}
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Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
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- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.
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