CVE-2026-34877
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 versions from 2.19.0 up to 3.6.5, Mbed TLS 4.0.0. Insufficient protection of serialized SSL context or session structures allows an attacker who can modify the serialized structures to induce memory corruption, leading to arbitrary code execution. This is caused by Incorrect Use of Privileged APIs.
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 contains a vulnerability in its SSL context and session serialization/deserialization code. Insufficient protection of serialized structures allows an attacker with the ability to modify serialized data to induce memory corruption and achieve arbitrary code execution. The vulnerability stems from incorrect use of privileged APIs during the serialization process.
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>= 2.19.0, < 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
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 versionLocate the Mbed TLS library in your environment and check its version identifier in the version header file or library metadata. Common locations include /usr/include/mbedtls/version.h or the library binary itself.Affected if The installed version is >= 2.19.0 and < 3.6.6, or exactly 4.0.0
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Determine if SSL context serialization is usedSearch your codebase or configuration for calls to mbedtls_ssl_context_save, mbedtls_ssl_context_load, or similar serialization functions that save or restore SSL context structures to/from persistent storage.Affected if Your application serializes and deserializes SSL context structures using Mbed TLS APIs
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Determine if session serialization is usedSearch your codebase or configuration for calls to mbedtls_ssl_session_save, mbedtls_ssl_session_load, or similar functions that serialize session data structures.Affected if Your application serializes and deserializes SSL session structures using Mbed TLS APIs
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Assess serialized data exposureExamine where serialized SSL contexts or sessions are stored or transmitted. Check file permissions on any saved session files, network transmission paths, or inter-process communication channels used for this data.Affected if Serialized SSL context or session data can be modified by an attacker due to lack of integrity verification or encryption
You are affected if you run Mbed TLS 2.19.0-3.6.5 or 4.0.0 AND your application uses SSL context or session serialization with data that could be tampered with by an attacker.
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
Upgrade Mbed TLS to a version beyond 3.6.5 (or the latest stable release) which contains the fix. Additionally, implement integrity verification (e.g., HMAC or signature validation) on serialized SSL context and session data before deserialization to detect tampering.
Mbed TLS 3.6.6 (or 4.0.1 if released for 4.x branch)
- 1. Identify the current Mbed TLS version in use by checking project dependencies or library files
- 2. For Mbed TLS 2.x versions (>=2.19.0): Upgrade to Mbed TLS 3.6.6 or later
- 3. For Mbed TLS 3.x versions (>=3.0.0, <3.6.6): Upgrade to Mbed TLS 3.6.6 or later
- 4. For Mbed TLS 4.0.0: Upgrade to Mbed TLS 4.0.1 or later (if available) or 3.6.6+
- 5. Rebuild and redeploy the application with the updated Mbed TLS library
- 6. Verify the upgrade by checking the library version at runtime
- 7. Test the application thoroughly to ensure SSL/TLS functionality remains operational
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation10.0 h
- Implementation20.0 h
- Testing20.0 h
- Review / QA12.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-34877 — 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-2026-34877 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
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- Version or environment caveats, and links to real fixes
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