CVE-2026-25833
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 3.5.0 to 3.6.5 fixed in 3.6.6 and 4.1.0 has a buffer overflow in the x509_inet_pton_ipv6() function
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 confidenceMbed TLS versions 3.5.0 through 3.6.5 contain a buffer overflow vulnerability in the x509_inet_pton_ipv6() function, which parses IPv6 addresses in X.509 certificates. This could allow remote attackers to cause a denial of service or potentially execute arbitrary code via specially crafted certificates with malformed IPv6 addresses.
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 versionCheck the installed Mbed TLS library version by examining libmbedtls.so, libmbedx509.so, or libmbedcrypto.so files, or run 'mbedtls_version' command if available. Also check any header files like 'include/mbedtls/version.h' for the version macro.Affected if The installed version is 3.5.0 through 3.6.5 inclusive, or version 4.0.0 exactly.
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Locate Mbed TLS in dependent applicationsUse 'ldd' on any application binaries that link against Mbed TLS to identify which programs load the vulnerable library, or check package manager listings for Mbed TLS packages.Affected if Any application dynamically links to a vulnerable version of libmbedtls, libmbedx509, or libmbedcrypto.
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Verify X.509 certificate parsing is in useReview application configuration and logs to determine if X.509 certificate validation is performed, particularly for client or server certificate verification. Check for use of mbedtls_x509_crt_parse or similar parsing functions.Affected if The environment processes X.509 certificates from untrusted sources, as the vulnerability triggers during IPv6 address parsing in certificates.
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Inspect certificate handling for IPv6 addressesExamine any stored or processed certificates for Subject Alternative Name (SAN) extensions or other fields containing IPv6 addresses. Use 'openssl x509 -text' to inspect certificate contents.Affected if Certificates containing IPv6 addresses in any field are being parsed by the vulnerable Mbed TLS code.
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Check for IPv6 network support enabledVerify if the system or applications have IPv6 enabled or configured, as the vulnerable code path handles IPv6 address conversion in certificate parsing.Affected if IPv6 is enabled in the system or applications, which triggers the vulnerable x509_inet_pton_ipv6() code path.
You are affected if your environment uses any version of Mbed TLS between 3.5.0 and 3.6.5 inclusive, or version 4.0.0, and processes X.509 certificates containing IPv6 addresses.
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 version 3.6.6 or 4.1.0 or later to resolve the buffer overflow vulnerability in the IPv6 address parsing function.
Mbed TLS 3.6.6 (for 3.x branch) or Mbed TLS 4.1.0 (for 4.x branch)
- Identify your current Mbed TLS version by checking your project's dependencies or library version
- If using Mbed TLS 3.x branch (versions 3.5.0 through 3.6.5): Upgrade to version 3.6.6 or later
- If using Mbed TLS 4.x branch (version 4.0.0): Upgrade to version 4.1.0 or later
- Update your dependency manager (e.g., package manager, build system, or submodule) to reference the fixed version
- Rebuild your project and verify the upgrade resolves the vulnerability
Generated from the published advisory — verify against the referenced sources before acting.
- 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-2026-25833 — 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-2026-25833 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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- 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
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