CVE-2026-22903
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 unauthenticated remote attacker can send a crafted HTTP request containing an overly long SESSIONID cookie. This can trigger a stack buffer overflow in the modified lighttpd server, causing it to crash and potentially enabling remote code execution due to missing stack protections.
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 confidenceAn unauthenticated remote attacker can send a crafted HTTP request with an oversized SESSIONID cookie that triggers a stack buffer overflow in a modified lighttpd server. The missing stack protection mechanisms (such as stack canaries, ASLR, or stack guards) make remote code execution feasible, in addition to denial of service via crash.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
CVSS 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 if you are running the modified lighttpd serverCheck the server banner or version output (e.g., lighttpd -v, HTTP Server header) and confirm it is a custom or modified version rather than upstream lighttpdAffected if Running a modified (non-upstream) version of lighttpd that contains the custom SESSIONID cookie handling code
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Determine the installed version of the modified lighttpdRun 'lighttpd -v' or check the package/software inventory for the version number of the modified lighttpd installationAffected if The version falls within any affected ranges if provided by your vendor, or if it is an unpatched version of the modified server
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Verify if SESSIONID cookie handling is enabledInspect the lighttpd configuration file (usually lighttpd.conf) for any directives related to SESSIONID cookie processing, session handling modules, or custom cookie parsing rulesAffected if SESSIONID cookie handling or custom session modules are enabled in the configuration
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Check for cookie length validationSearch configuration files for any max cookie size, cookie length limits, or session ID length restrictions; also check if any WAF or input validation layer is presentAffected if No length validation is enforced on the SESSIONID cookie value, allowing arbitrarily large values to be processed
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Monitor for crash logs or anomalous behaviorReview server logs for sudden crashes, segfaults, or abnormal termination events that coincide with requests containing large cookie valuesAffected if The server has crashed or exhibited unstable behavior potentially caused by this overflow
You are likely affected if you are running a modified lighttpd server with SESSIONID cookie handling enabled and no length limits on cookie values, particularly if the version is unpatched.
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.
From vendor dataApply patches or update to a fixed version of the modified lighttpd server; implement input validation to enforce reasonable length limits on the SESSIONID cookie; consider deploying a WAF rule to block requests with abnormally large cookie values as an interim measure.
- Consultation3.0 h
- Implementation6.0 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 $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-22903 — 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-2026-22903 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
- No spam, self-promotion, credentials, or personal data