Microsoft · 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
Affects MicrosoftSource GCVE Database
Not known to be exploited · CVSS 5.1 Medium.
Data as of 26 Oct 2026, 08:30 UTC
- EPSS
- 0.2% chance of exploitation in 30 days – higher than 19% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Exploitation evidence
Disclosed: evidence found.
CVE published 1 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
GitHubmbed-tls/mbedtlspkg:github/mbed-tls/mbedtlsOther threats | Affected
| Fixed in– |
GitHubmbed-tls/TF-PSA-Cryptopkg:github/mbed-tls/TF-PSA-CryptoOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
Until a fix is available, users should consider disabling LLVM's select-optimize feature during compilation or avoid using affected versions of Mbed TLS and TF-PSA-Crypto with this compiler optimization enabled. Monitor official Microsoft Security Response Center advisories for updates.
Description
CVE-2025-66442 is a compiler-induced timing side channel vulnerability affecting Mbed TLS through version 4.0.0 and TF-PSA-Crypto through version 1.0.0. This issue occurs specifically when LLVM's select-optimize feature is used, impacting RSA and CBC/ECB decryption operations. The vulnerability is related to improper handling of timing variations introduced by compiler optimizations. No CVSS score or patch information is provided, and no known exploits are reported in the wild. The affected software includes Mbed TLS versions up to 4.0.0 and TF-PSA-Crypto up to 1.0.0. The vulnerability is categorized under CWE-385 (Timing Side Channel).