CVE-2026-43929
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 · uneditedssrfcheck is a library that checks if a string contains a potential SSRF attack. In 1.3.0 and earlier, ssrfcheck fails to block Server-Side Request Forgery attacks when the target private IP address is encoded as an IPv4-mapped IPv6 address (e.g. http://[::ffff:127.0.0.1]/). The WHATWG URL parser built into Node.js silently normalizes the IPv4 notation inside the brackets to compressed hex form ([::ffff:7f00:1]) before the library's private-IP regex ever runs. The regex was written to match dot-notation only and therefore never matches any real input — all seven IANA private IPv4 ranges, including the AWS/GCP/Azure metadata address 169.254.169.254, are bypassed. Any application using isSSRFSafeURL() to guard HTTP requests made with user-supplied URLs is fully exposed to SSRF.
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 confidenceThe ssrfcheck library (v1.3.0 and earlier) fails to detect SSRF when private IPv4 addresses are encoded as IPv6-mapped addresses (e.g., http://[::ffff:127.0.0.1]/). The Node.js WHATWG URL parser normalizes these to hex form ([::ffff:7f00:1]) before the library's regex runs, but the regex only matches dot-notation IPv4 and never matches the normalized form, bypassing all seven IANA private IPv4 ranges including cloud metadata endpoints like 169.254.169.254.
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
- Low
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
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.
-
Identify if ssrfcheck is usedSearch your project for 'ssrfcheck' in package.json dependencies, package-lock.json, or node_modules directory. Run: grep -r 'ssrfcheck' package.json package-lock.json 2>/dev/null || find node_modules -name 'ssrfcheck' -type d 2>/dev/nullAffected if ssrfcheck is found in dependencies or node_modules
-
Check ssrfcheck versionRun: npm list ssrfcheck (if using npm) or inspect the version field in node_modules/ssrfcheck/package.jsonAffected if Version is 1.3.0 or earlier, or version field cannot be determined (indicating very old release)
-
Verify URL processing with IPv6Inspect your code where ssrfcheck is called: look for URL validation functions that pass user-controlled URLs to ssrfcheck.validate() or similar. Check if your application accepts URLs that could contain IPv6 brackets like http://[::ffff:127.0.0.1]/Affected if Your code passes URLs to ssrfcheck for SSRF protection and those URLs could originate from user input
-
Test IPv4-mapped IPv6 bypassCreate a test: pass http://[::ffff:127.0.0.1]/ or http://[::ffff:7f00:1]/ to ssrfcheck's validation function and observe if it blocks or allows the requestAffected if ssrfcheck allows these URLs (returns no error or true) when it should block them as private IP addresses
-
Confirm regex-only detectionExamine the ssrfcheck source code in node_modules/ssrfcheck/lib/ or similar path. Look for regex patterns that match only dot-notation IPv4 (e.g., 127.0.0.1) and do not handle IPv6 forms like ::ffff:127.0.0.1 or [::ffff:7f00:1]Affected if The library uses regex that exclusively matches decimal-dot IPv4 notation without IPv6 handling
You are affected if your project uses ssrfcheck v1.3.0 or earlier and passes user-controlled URLs through it, because the library fails to block IPv4-mapped IPv6 addresses representing private ranges.
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 dataUpdate ssrfcheck to validate URLs after WHATWG normalization and add regex patterns to detect IPv6-mapped IPv4 addresses, or migrate to a SSRF protection library that properly handles IPv6 address families.
- Consultation3.0 h
- Implementation6.0 h
- Testing5.0 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 $4,464.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-43929 — 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-2026-43929 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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