CVE-2026-29078
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 · uneditedLexbor is a web browser engine library. Prior to 2.7.0, the ISO‑2022‑JP encoder in Lexbor fails to reset the temporary size variable between iterations. The statement ctx->buffer_used -= size with a stale size = 3 causes an integer underflow that wraps to SIZE_MAX. Afterwards, memcpy is called with a negative length, leading to an out‑of‑bounds read from the stack and an out‑of‑bounds write to the heap. The source data is partially controllable via the contents of the DOM tree. This vulnerability is fixed in 2.7.0.
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 · high confidenceInteger underflow in Lexbor's ISO-2022-JP encoder occurs when the temporary size variable is not reset between iterations. The stale size value of 3 causes ctx->buffer_used to underflow to SIZE_MAX, leading memcpy to be called with a negative length. This results in out-of-bounds reads from the stack and out-of-bounds writes to the heap, with partial control over source data via DOM tree contents.
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< 2.7.0CVSS 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 Lexbor installationLocate the Lexbor library in your environment. Check for Lexbor headers, shared libraries, or package dependencies in your project.Affected if Lexbor library is present in the environment
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Determine installed Lexbor versionRetrieve the Lexbor version from package manager, library headers, or version information. Compare against the affected range: versions prior to 2.7.0.Affected if The installed version is less than 2.7.0
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Verify ISO-2022-JP encoding is in useInspect application code or configuration to determine if ISO-2022-JP encoding is being invoked. Look for text encoding, character conversion, or DOM serialization routines using this specific Japanese encoding.Affected if ISO-2022-JP encoding is actively used with a vulnerable Lexbor version
Environment is affected only if Lexbor version is below 2.7.0 AND the ISO-2022-JP encoder is being used for text processing.
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 · scoped2.7.0
Upgrade Lexbor to version 2.7.0 or later, which properly resets the temporary size variable between encoder iterations.
2.7.0
- Identify the Lexbor library version currently in use by checking project dependencies or library files
- Upgrade Lexbor to version 2.7.0 or later using the appropriate package manager or build system (e.g., pip install lexbor>=2.7.0, composer require lexbor>=2.7.0, or rebuild from source)
- Verify the upgrade was successful by checking the installed Lexbor version
- Test the application to ensure the ISO-2022-JP encoding functionality works correctly with the updated library
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-29078 — 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-2026-29078 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
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