CVE-2025-66442
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedIn 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · moderate confidenceMbed TLS through 4.0.0 and TF-PSA-Crypto through 1.0.0 contain a compiler-induced timing side channel in RSA and CBC/ECB decryption operations. The vulnerability manifests only when compiling with LLVM's select-optimize feature enabled, which causes the compiler to generate code with observable timing differences that could leak sensitive cryptographic information through a timing attack.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data<= 4.0.0<= 1.0.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
-
Identify Mbed TLS or TF-PSA-Crypto versionLocate the library binary or source code and check the version string, typically found in version header files or by inspecting the compiled library metadataAffected if The installed version is Mbed TLS <= 4.0.0 or TF-PSA-Crypto <= 1.0.0
-
Determine compilation toolchainInspect the build configuration, Makefile, or compile flags used when building the library to identify if LLVM/clang was used as the compilerAffected if The library was compiled using LLVM/clang as the C compiler
-
Check for select-optimize flagReview the build logs, CMake configuration, or compiler flags passed during compilation for the presence of -mllvm -select-optimize or similar LLVM optimization flagsAffected if The compilation flags include LLVM select-optimize optimization (mllvm select-optimize or equivalent)
-
Verify RSA or CBC/ECB decryption is in useReview application code or runtime configuration to confirm whether RSA decryption operations or CBC/ECB mode decryption is being performed using the affected libraryAffected if The application performs RSA decryption or uses CBC/ECB decryption modes with the affected library
You are affected if you are using Mbed TLS <= 4.0.0 or TF-PSA-Crypto <= 1.0.0 that was compiled with LLVM's select-optimize flag enabled AND your application uses RSA decryption or CBC/ECB decryption operations
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataDisable LLVM's select-optimize flag when compiling affected Mbed TLS or TF-PSA-Crypto versions, or upgrade to a patched version that addresses the compiler-induced timing leakage in cryptographic operations.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,808.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-66442 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2025-66442 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data