CVE-2025-27809
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 · uneditedMbed TLS before 2.28.10 and 3.x before 3.6.3, on the client side, accepts servers that have trusted certificates for arbitrary hostnames unless the TLS client application calls mbedtls_ssl_set_hostname.
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 · high confidenceIn Mbed TLS clients, certificate hostname verification is not enforced by default. If an application does not explicitly call mbedtls_ssl_set_hostname() before establishing a TLS connection, the library will accept certificates trusted by the local CA store even if the certificate's Common Name or Subject Alternative Name does not match the target hostname. This allows MITM attacks using any valid CA-signed certificate.
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< 2.28.10>= 3.0.0, < 3.6.3CVSS 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
- Network
- Complexity
- High
- Privileges
- None
- User interaction
- None
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/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.
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Identify Mbed TLS library presenceSearch for Mbed TLS library files (e.g., libmbedtls.so, libmbedcrypto.so) or headers (e.g., mbedtls/ssl.h) in the system or application dependenciesAffected if Mbed TLS library is not found - the product may not be affected or may use a different TLS library
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Determine installed Mbed TLS versionCheck library version via package manager, library file version info, or version header (e.g., mbedtls/version.h). Compare against affected ranges: Arm Mbed TLS < 2.28.10 or Trustedfirmware Mbed TLS >= 3.0.0 and < 3.6.3Affected if Version falls within the affected ranges and the application does not explicitly call mbedtls_ssl_set_hostname() before TLS connections
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Identify the Mbed TLS flavorCheck if using Arm Mbed TLS or Trustedfirmware Mbed TLS by examining library packaging, documentation, or version string prefix (TF- for Trustedfirmware)Affected if Using a vulnerable version of either flavor without proper hostname verification calls
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Audit application code for hostname verification callsSearch source code for calls to mbedtls_ssl_set_hostname() or mbedtls_ssl_set_hostname_lwip() before mbedtls_ssl_handshake() in all TLS client code pathsAffected if The application does NOT call mbedtls_ssl_set_hostname() with the intended target hostname before establishing TLS connections - this is the vulnerable condition regardless of version
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Verify runtime configuration or wrapper usageIf using a higher-level wrapper or framework that wraps Mbed TLS, check whether that wrapper internally calls mbedtls_ssl_set_hostname() or exposes hostname verification optionsAffected if The wrapper does not enforce hostname verification and the application does not directly call mbedtls_ssl_set_hostname()
You are affected if you use a vulnerable Mbed TLS version AND your application code does not explicitly call mbedtls_ssl_set_hostname() with the target hostname before establishing TLS connections.
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.
dbcve · scoped2.28.103.6.3
Ensure all Mbed TLS client code calls mbedtls_ssl_set_hostname() with the intended target hostname before establishing connections, or upgrade to Mbed TLS 2.28.10/3.6.3 if a default-enforcement fix was included.
Mbed TLS 2.28.10 for 2.x branch or Mbed TLS 3.6.3 for 3.x branch
- Identify the current Mbed TLS version in use by checking project dependencies or library version
- Determine which Mbed TLS branch (2.x or 3.x) is currently in use
- For Mbed TLS 2.x users: upgrade to version 2.28.10 or later
- For Mbed TLS 3.x users: upgrade to version 3.6.3 or later
- Update the dependency management system (e.g., package.json, requirements.txt, CMake, or submodule) to specify the fixed version
- Rebuild and redeploy the application with the updated Mbed TLS library
- Verify that TLS certificate validation now properly checks hostname matching by testing against a certificate for a different hostname
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 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 $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2025-27809 — 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-2025-27809 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
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- Version or environment caveats, and links to real fixes
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