Bug 2453966 (CVE-2026-34872)

Summary: CVE-2026-34872 mbedtls: Mbed TLS and TF-PSA-Crypto: Shared secret manipulation via improper FFDH input validation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Mbed TLS and TF-PSA-Crypto. This vulnerability, stemming from improper input validation in the finite-field Diffie-Hellman (FFDH) key exchange, allows a remote attacker to force the shared secret into a small, predictable set of values. This lack of contributory behavior can compromise the security of protocols that rely on the uniqueness and unpredictability of shared secrets, potentially enabling further attacks.
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oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
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Bug Depends On: 2454195, 2454198, 2454200, 2454204, 2454208    
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Description OSIDB Bzimport 2026-04-01 20:01:49 UTC 
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).