High
mbedtls — security advisory
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.
- Products
- mbedtls
- Affected versions
- 2.1.2-1, 2.16.11-0.1ubuntu1, 2.16.11-0.3, 2.16.2-1, 2.16.3-1, 2.16.4-1ubuntu2, 2.16.4-1ubuntu2+esm1, 2.16.9-0.1ubuntu1, 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, 2.28.0-1, 2.28.0-1build1, 2.28.0-1ubuntu0.1~esm1, 2.28.3-1, 2.28.6-1ubuntu1, 2.28.7-1.1ubuntu1, 2.28.7-1ubuntu1, 2.28.8-1, 2.28.8-1ubuntu0.1~esm1, 2.5.1-1ubuntu1, 2.6.0-1, 2.7.0-2, 2.8.0-1, 2.8.0-1ubuntu0.1~esm1, 3.6.2-3ubuntu1, 3.6.5-0.1ubuntu1, 3.6.5-0.1ubuntu2, 3.6.6-0.1ubuntu1, 3.6.7-3ubuntu1
- Fixed versions
- Not specified
- CVEs
- CVE-2026-34876
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 31 Oct 2026, 03:01 UTC · Revision 1
Source evidence
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.
osv:UBUNTU-CVE-2026-34876
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
mbedtls
Fixed versions: Not specified
Complete source record
{
"id": "cb53e88d949b034eea73e636e2b1774c9de9d18c0d3a8ed653099c32f4d56739",
"url": "https://osv.dev/vulnerability/UBUNTU-CVE-2026-34876",
"method": "structured",
"payload": {
"kind": "advisory",
"title": "UBUNTU-CVE-2026-34876",
"summary": "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.",
"evidence": "osv:UBUNTU-CVE-2026-34876",
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{
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{
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{
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{
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{
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}
],
"severity": "high",
"structured": {
"id": "UBUNTU-CVE-2026-34876",
"aliases": [
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],
"metrics": [
{
"type": "CVSS_V3",
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N"
},
{
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"score": "medium"
}
],
"affected": [
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},
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},
{
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{
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],
"modified": "2026-10-17T13:00:02.294038682Z",
"provider": "osv",
"upstream": [
"CVE-2026-34876"
],
"references": [
"https://ubuntu.com/security/CVE-2026-34876",
"https://www.cve.org/CVERecord?id=CVE-2026-34876",
"https://mbed-tls.readthedocs.io/en/latest/security-advisories/mbedtls-security-advisory-2026-03-ccm-finish-boundary-check/"
]
},
"related_cves": [
{
"value": "CVE-2026-34876",
"evidence": "/upstream"
}
],
"security_relevant": true,
"severity_evidence": "/severity/0/score"
},
"source_id": "core-osv",
"document_id": 360165,
"published_at": "2026-04-02T16:16:00+00:00"
}