CVE-2009-4881
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 · uneditedInteger overflow in the __vstrfmon_l function in stdlib/strfmon_l.c in the strfmon implementation in the GNU C Library (aka glibc or libc6) before 2.10.1 allows context-dependent attackers to cause a denial of service (application crash) via a crafted format string, as demonstrated by the %99999999999999999999n string, a related issue to CVE-2008-1391.
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 overflow in the __vstrfmon_l function in glibc's strfmon implementation allows denial of service via crafted format strings with extremely large width specifiers (e.g., %99999999999999999999n). The overflow occurs when parsing the width field, potentially leading to buffer overflow and application crash.
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<= 2.9= 1.00= 1.01= 1.02= 1.03= 1.04= 1.05= 1.06= 1.07= 1.08= 1.09= 2.0CVSS 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
- Authentication
- None
- Confidentiality
- None
- Integrity
- None
- Availability
- Partial
AV:N/AC:L/Au:N/C:N/I:N/A:P
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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Determine installed glibc versionRun `ldd --version` or check `/lib/libc.so.6` (or /lib64/libc.so.6 on 64-bit systems) using `strings libc.so.6 | grep 'GNU libc'` to extract the version stringAffected if Version is 2.9 or earlier, or matches one of the listed affected versions (1.00 through 2.0)
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Identify applications using strfmonSearch application source code for calls to strfmon, strfmon_l, __vstrfmon_l, or similar functions from the strfmon family using `grep -r 'strfmon' /path/to/source`Affected if The application links against glibc and calls strfmon with format strings that could contain user-supplied width specifiers
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Check for user-controlled format string inputReview code paths where strfmon is called and trace whether the format string or its width specifiers originate from untrusted input (e.g., user input, network data, files)Affected if Untrusted input can reach the format string parameter of strfmon without sanitization
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Test for large width specifier handlingIf you have access to test the application, invoke it with a format string containing an extremely large width like %99999999999999999n and observe whether it crashes or behaves unexpectedlyAffected if Application crashes or exhibits buffer overflow behavior when processing large width specifiers
You are affected if your system runs glibc version 2.9 or earlier AND any application on that system uses strfmon with format strings that can be influenced by untrusted input.
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 dataUpgrade glibc to version 2.10.1 or later to obtain the patched version. For legacy systems where upgrade is not feasible, implement input validation to reject format strings containing unreasonably large width specifiers before passing to strfmon.
- Consultation2.0 h
- Implementation4.0 h
- Testing8.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2009-4881 — 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-2009-4881 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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- Version or environment caveats, and links to real fixes
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