CVE-2026-34874
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 · uneditedAn issue was discovered in Mbed TLS through 3.6.5 and 4.x through 4.0.0. There is a NULL pointer dereference in distinguished name parsing that allows an attacker to write to address 0.
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 confidenceA NULL pointer dereference vulnerability exists in Mbed TLS versions 3.x through 3.6.5 and 4.x through 4.0.0 during distinguished name (DN) parsing, typically in X.509 certificate handling. The vulnerability allows an attacker to write to memory address 0, potentially causing denial of service or enabling further exploitation.
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>= 3.5.0, < 3.6.6= 4.0.0CVSS 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
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
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 versionLocate and inspect the Mbed TLS library file or header (commonly libmbedcrypto, mbedtls/version.h, or the embedded version string) to determine the exact version number compiled into your applicationAffected if The version is 3.5.0 through 3.6.5, or exactly 4.0.0
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Confirm X.509 certificate parsing is in useReview application code or build configuration to determine whether the X.509 certificate parser module (mbedtls_x509_crt_parse or related functions) is linked and invoked at runtimeAffected if X.509 certificate parsing is enabled and used to load or validate certificates
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Check for distinguished name (DN) field processingInspect certificate handling code paths for calls that parse subject/issuer DN fields (such as mbedtls_x509_dn_gets or similar DN extraction functions) from certificatesAffected if The application parses or extracts DN fields from X.509 certificates
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Verify certificate input sourcesDetermine if the application accepts or processes certificates from untrusted sources (e.g., TLS connections, imported files, external APIs) that could supply specially crafted certificatesAffected if Certificates from external or untrusted sources are processed without prior validation
Your environment is affected if Mbed TLS version is 3.5.0 through 3.6.5 or 4.0.0 AND your application processes X.509 certificates containing DN fields from potentially untrusted input.
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 · scoped3.6.6
Update Mbed TLS to the latest version incorporating the fix for NULL pointer validation in distinguished name parsing. If immediate patching is not feasible, validate and sanitize certificate inputs before processing to reduce attack surface.
Mbed TLS 3.6.6 or later for 3.x branch; latest stable 4.x release for 4.x branch
- 1. Identify the current Mbed TLS version in use by checking project dependencies or library version header
- 2. For Mbed TLS 3.x branch (versions 3.5.0 through 3.6.5): upgrade to version 3.6.6 or later
- 3. For Mbed TLS 4.x branch (version 4.0.0): upgrade to the latest stable 4.x release that follows 4.0.0
- 4. Verify the upgrade by rebuilding the project and running existing test suites
- 5. Test TLS functionality with certificate handling, particularly any code that parses distinguished names (DN) from certificates
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation2.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-34874 — 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-2026-34874 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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