Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade') Affecting mbedtls package, versions [3.5.0,3.6.6)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-CONAN-MBEDTLS-15929027
- published8 Apr 2026
- disclosed1 Apr 2026
- creditJaehun Lee
Introduced: 1 Apr 2026
NewCVE-2026-34873 (opens in a new tab)How to fix?
Upgrade mbedtls to version 3.6.6 or higher.
Overview
Affected versions of this package are vulnerable to Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade') in the TLS 1.3 session resumption logic if the subsequent ClientHello negotiates TLS 1.2 back. An attacker can gain unauthorized access by impersonating a legitimate client during session resumption. This is only exploitable if client-side TLS 1.3 session resumption is enabled.