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CVE-2026-34872

30
FAUCET Score

CVE-2026-34872 is a critical vulnerability affecting Mbed TLS versions 3.5.x, 3.6.x through 3.6.5, and TF-PSA-Crypto 1.0. This flaw, rated 9.1 Critical, is due to improper input validation in Finite-Field Diffie-Hellman (FFDH), allowing an attacker to force the shared secret into a small set of values, impacting confidentiality and integrity. The vulnerability is network-exploitable with low attack complexity and can be leveraged by a peer or an active network attacker, though protocols like TLS are not dependent on the affected contributory behavior. There is currently no evidence of active exploitation, public exploit code, or significant community attention.

Impacted Technologies

VendorProductVersion(s)CPE
< 3.6.6CPE matchmatch criteria
cpe:2.3:a:arm:mbed_tls:*:*:*:*:*:*:*:*
1.0.0CPE matchmatch criteria
cpe:2.3:a:arm:tf-psa-crypto:1.0.0:-:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.1CRITICAL

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
NONE
Exploitability Score
3.9
Impact Score
5.2
CvssVersion
3.1

Exploit Intelligence

EPSS Score
0.20%
Probability of exploitation in next 30 days
EPSS Percentile
10.6%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0020 is in the 0th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Vendor Advisories (1)

microsoft2026-Apr/CVE-2026-34872Moderate

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).

Apr 14, 2026

References

mbed-tls.readthedocs.io / en/latest/security-advisories
Vendor Advisory
mbed-tls.readthedocs.io / en/latest/security-advisories/mbedtls-security-advisory-2026-03-ffdh-peerkey-checks
MitigationVendor Advisory