CVE-2026-34876
published 2026-04-02CVE-2026-34876: 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…
PriorityP347high7.5CVSS 3.1
AVNACLPRNUINSUCHINAN
EPSS
0.39%
31.8th percentile
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.
Affected
2 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | mbedtls | — | — |
| trustedfirmware | mbed_tls | >= 3.1.0 < 3.6.6 | 3.6.6 |
CVSS provenance
nvdv3.17.5HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
osv7.5HIGH
vendor_debian7.5HIGH
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OSV
CVE-2026-34876: (An issue was discovered in Mbed TLS 3
osv·2026-04-03·CVSS 7.5
CVE-2026-34876 [HIGH] CVE-2026-34876: (An issue was discovered in Mbed TLS 3
(An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds ...)
GHSA
GHSA-jw9g-6hxw-4whq: An issue was discovered in Mbed TLS 3
ghsa_unreviewed·2026-04-02
CVE-2026-34876 [HIGH] CWE-125 GHSA-jw9g-6hxw-4whq: An issue was discovered in Mbed TLS 3
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
CVE-2026-34876: An issue was discovered in Mbed TLS 3
osv·2026-04-02·CVSS 7.5
CVE-2026-34876 [HIGH] CVE-2026-34876: An issue was discovered in Mbed TLS 3
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.
Debian
CVE-2026-34876: mbedtls - An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vuln...
vendor_debian·2026·CVSS 7.5
CVE-2026-34876 [HIGH] CVE-2026-34876: mbedtls - An issue was discovered in Mbed TLS 3.x before 3.6.6. An out-of-bounds read vuln...
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.
Scope: local
bookworm: open
bu
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-34876 micropython: CCM multipart finish tag-length validation bypass [fedora-all]
bugzilla·2026-04-02·CVSS 7.5
CVE-2026-34876 [HIGH] CVE-2026-34876 micropython: CCM multipart finish tag-length validation bypass [fedora-all]
CVE-2026-34876 micropython: CCM multipart finish tag-length validation bypass [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This is an mbedtls CVE, micropython is not affected as the relevant code is not compiled.
Bugzilla
CVE-2026-34876 rust-psa-crypto-sys: CCM multipart finish tag-length validation bypass [fedora-all]
bugzilla·2026-04-02·CVSS 7.5
CVE-2026-34876 [HIGH] CVE-2026-34876 rust-psa-crypto-sys: CCM multipart finish tag-length validation bypass [fedora-all]
CVE-2026-34876 rust-psa-crypto-sys: CCM multipart finish tag-length validation bypass [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Discussion:
This package has changed maintainer in Fedora. Reassigning to the new maintainer of this component.
---
This package is not present in any active branch of Fedora.
Bugzilla
CVE-2026-34876 mbedtls: CCM multipart finish tag-length validation bypass [fedora-all]
bugzilla·2026-04-02·CVSS 7.5
CVE-2026-34876 [HIGH] CVE-2026-34876 mbedtls: CCM multipart finish tag-length validation bypass [fedora-all]
CVE-2026-34876 mbedtls: CCM multipart finish tag-length validation bypass [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Wiz
CVE-2026-34873 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34873 [MEDIUM] CVE-2026-34873 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34873 :
Mbed TLS vulnerability analysis and mitigation
An issue was discovered in Mbed TLS 3.5.0 through 4.0.0. Client impersonation can occur while resuming a TLS 1.3 session.
Source : NVD
## 9.1
Score
Published April 1, 2026
Severity CRITICAL
CNA Score 9.1
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 10.6
Exploitation Probability (EPSS) N/A
Affected packages and libraries
mbedtls
Sources
NVD
Debian 11, 12, 13, 14 Severity CRITICAL No Fix Added at: Apr 02, 2026
Echo Severity CRITICAL No Fix Added at: Apr 02, 2026
## Get a CVE risk assessment
Get a prioritized view of CVEs in your cloud—so you can focus on what's exploitable, not
Wiz
CVE-2026-34871 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34871 [MEDIUM] CVE-2026-34871 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34871 :
Mbed TLS vulnerability analysis and mitigation
An issue was discovered in Mbed TLS before 3.6.6 and 4.x before 4.1.0 and TF-PSA-Crypto before 1.1.0. There is a Predictable Seed in a Pseudo-Random Number Generator (PRNG).
Source : NVD
## 6.7
Score
Published April 1, 2026
Severity MEDIUM
CNA Score 6.7
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 2.7
Exploitation Probability (EPSS) N/A
Affected packages and libraries
cpe:2.3:a:arm:mbed_tls
mbedtls
Sources
Debian 11, 12, 13, 14 Severity MEDIUM No Fix Added at: Apr 02, 2026
Echo Severity MEDIUM No Fix Added at: Apr 02, 2026
Linux Severity MEDIUM Has Fix Added at: Apr 06, 2026
Li
Wiz
CVE-2026-25835 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-25835 [MEDIUM] CVE-2026-25835 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-25835 :
Mbed TLS vulnerability analysis and mitigation
Mbed TLS before 3.6.6 and TF-PSA-Crypto before 1.1.0 misuse seeds in a Pseudo-Random Number Generator (PRNG).
Source : NVD
## 7.7
Score
Published April 1, 2026
Severity HIGH
CNA Score 7.7
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 2.7
Exploitation Probability (EPSS) N/A
Affected packages and libraries
cpe:2.3:a:arm:mbed_tls
mbedtls
Sources
Alpine 3.20, 3.21, 3.22, 3.23, edge Severity HIGH Has Fix Added at: Apr 02, 2026
Debian 11, 12, 13, 14 Severity HIGH No Fix Added at: Apr 05, 2026
Echo Severity HIGH No Fix Added at: Apr 05, 2026
Linux Severity HIGH Has Fix Added at: Apr 06
Wiz
CVE-2026-34876 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34876 [MEDIUM] CVE-2026-34876 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34876 :
Mbed TLS vulnerability analysis and mitigation
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-leve
Wiz
CVE-2026-25833 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-25833 [MEDIUM] CVE-2026-25833 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-25833 :
Mbed TLS vulnerability analysis and mitigation
Mbed TLS 3.5.0 to 3.6.5 fixed in 3.6.6 and 4.1.0 has a buffer overflow in the x509_inet_pton_ipv6() function
Source : NVD
## 7.5
Score
Published April 1, 2026
Severity HIGH
CNA Score 7.5
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 15.2
Exploitation Probability (EPSS) N/A
Affected packages and libraries
mbedtls
cpe:2.3:a:arm:mbed_tls
Sources
Alpine 3.20, 3.21, 3.22, 3.23, edge Severity HIGH Has Fix Added at: Apr 02, 2026
Debian 11, 12, 13, 14 Severity HIGH No Fix Added at: Apr 05, 2026
Echo Severity HIGH No Fix Added at: Apr 05, 2026
Linux Severity HIGH Has Fix Added at: Apr 06
Wiz
CVE-2026-34877 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34877 [MEDIUM] CVE-2026-34877 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34877 :
Mbed TLS vulnerability analysis and mitigation
An issue was discovered in Mbed TLS versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.
Source : NVD
## 9.8
Score
Published April 2, 2026
Severity CRITICAL
CNA Score 9.8
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 30
Exploitation Probability (EPSS) 0.1
Affected packages and libraries
mbedtls
cpe:2.3:a:arm:mbed_tls
Sources
Debian 11, 12,
Wiz
CVE-2026-34875 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34875 [MEDIUM] CVE-2026-34875 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34875 :
Mbed TLS vulnerability analysis and mitigation
An issue was discovered in Mbed TLS through 3.6.5 and TF-PSA-Crypto 1.0.0. A buffer overflow can occur in public key export for FFDH keys.
Source : NVD
## 9.8
Score
Published April 1, 2026
Severity CRITICAL
CNA Score 9.8
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 16.4
Exploitation Probability (EPSS) 0.1
Affected packages and libraries
cpe:2.3:a:arm:mbed_tls
mbedtls
Sources
Debian 11, 12, 13, 14 Severity CRITICAL No Fix Added at: Apr 02, 2026
Echo Severity CRITICAL No Fix Added at: Apr 02, 2026
Linux Severity CRITICAL Has Fix Added at: Apr 06, 2026
Linux Severity CRITICAL Has
Wiz
CVE-2026-34872 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34872 [MEDIUM] CVE-2026-34872 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34872 :
Mbed TLS vulnerability analysis and mitigation
An issue was discovered in Mbed TLS 3.5.x and 3.6.x through 3.6.5 and TF-PSA-Crypto 1.0. There is a lack of contributory behavior in FFDH due to improper input validation. Using finite-field Diffie-Hellman, the other party can force the shared secret into a small set of values (lack of contributory behavior). This is a problem for protocols that depend on contributory behavior (which is not the case for TLS). The attack can be carried by the peer, or depending on the protocol by an active network attacker (person in the middle).
Source : NVD
## 9.1
Score
Published April 1, 2026
Severity CRITICAL
CNA Score 9.1
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/
Wiz
CVE-2025-66442 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2025-66442 [MEDIUM] CVE-2025-66442 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2025-66442 :
Mbed TLS vulnerability analysis and mitigation
In Mbed TLS through 4.0.0, there is a compiler-induced timing side channel (in RSA and CBC/ECB decryption) that only occurs with LLVM's select-optimize feature. TF-PSA-Crypto through 1.0.0 is also affected.
Source : NVD
## 5.1
Score
Published April 1, 2026
Severity MEDIUM
CNA Score 5.1
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 5.7
Exploitation Probability (EPSS) N/A
Affected packages and libraries
mbedtls
cpe:2.3:a:arm:mbed_tls
Sources
Debian 11, 12, 13, 14 Severity MEDIUM No Fix Added at: Apr 05, 2026
Echo Severity MEDIUM No Fix Added at: Apr 05, 2026
Linux Severity MEDIUM N
Wiz
CVE-2026-34874 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-34874 [MEDIUM] CVE-2026-34874 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-34874 :
Mbed TLS vulnerability analysis and mitigation
An issue was discovered in Mbed TLS through 3.6.5 and 4.x through 4.0.0. There is a NULL pointer dereference in distinguished name parsing that allows an attacker to write to address 0.
Source : NVD
## 7.5
Score
Published April 1, 2026
Severity HIGH
CNA Score 7.5
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 22
Exploitation Probability (EPSS) 0.1
Affected packages and libraries
mbedtls
cpe:2.3:a:arm:mbed_tls
Sources
Debian 11, 12, 13, 14 Severity HIGH No Fix Added at: Apr 02, 2026
Echo Severity HIGH No Fix Added at: Apr 02, 2026
Linux Severity HIGH Has Fix Added at: Apr 05, 2026
Wiz
CVE-2026-25834 Impact, Exploitability, and Mitigation Steps | Wiz
blogs_wiz·CVSS 5.1
CVE-2026-25834 [MEDIUM] CVE-2026-25834 Impact, Exploitability, and Mitigation Steps | Wiz
## CVE-2026-25834 :
Mbed TLS vulnerability analysis and mitigation
Mbed TLS v3.3.0 up to 3.6.5 and 4.0.0 allows Algorithm Downgrade.
Source : NVD
## 6.5
Score
Published April 1, 2026
Severity MEDIUM
CNA Score 6.5
Affected Technologies
Mbed TLS
Has Public Exploit No
Has CISA KEV Exploit No
CISA KEV Release Date N/A
CISA KEV Due Date N/A
Exploitation Probability Percentile (EPSS) 5.1
Exploitation Probability (EPSS) N/A
Affected packages and libraries
cpe:2.3:a:arm:mbed_tls
mbedtls
Sources
Alpine 3.20, 3.21, 3.22, 3.23, edge Severity MEDIUM Has Fix Added at: Apr 02, 2026
Debian 11, 12, 13, 14 Severity MEDIUM No Fix Added at: Apr 05, 2026
Echo Severity MEDIUM No Fix Added at: Apr 05, 2026
Linux Severity MEDIUM Has Fix Added at: Apr 06, 2026
Linux Severity MEDIUM Has
2026-04-02
Published