HTTP ServerWeb server / proxy · Apache
CVE-2001-1556
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 · uneditedThe log files in Apache web server contain information directly supplied by clients and does not filter or quote control characters, which could allow remote attackers to hide HTTP requests and spoof source IP addresses when logs are viewed with UNIX programs such as cat, tail, and grep.
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 confidenceApache web server logs client-supplied HTTP request data without filtering or quoting control characters. This allows remote attackers to inject special characters that can hide requests or spoof source IP addresses when logs are viewed with UNIX utilities like cat, tail, and grep.
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
HTTP ServerWeb server / proxy
>= 1.3.0, < 1.3.31>= 2.0.0, < 2.0.49CVSS 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
- Partial
- Availability
- None
AV:N/AC:L/Au:N/C:N/I:P/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.
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Determine installed Apache versionRun 'httpd -v' (or 'apache2 -v' on Debian-based systems) to retrieve the server version. On Windows, check the version via the Apache Service Monitor or run 'httpd.exe -v'.Affected if The version displayed is 1.3.0 through 1.3.30, or 2.0.0 through 2.0.48.
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Verify Apache is running and logging is enabledCheck if the httpd/apache2 process is active and confirm that the default access log (typically /var/log/httpd/access_log or /var/log/apache2/access.log) exists and is being written to.Affected if Apache is running with default logging enabled, as the vulnerability affects the default logging behavior.
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Examine log entries for control character injectionUse 'od -c' or 'hexdump -C' on recent access log entries to inspect whether raw bytes including control characters (bytes 0x00-0x1F, 0x7F) are present in the request field portion of the log.Affected if Control characters appear unfiltered in the logged request data, indicating the vulnerability is present.
If Apache version falls within 1.3.0-1.3.30 or 2.0.0-2.0.48 and logging is active with unfiltered control characters visible in raw log inspection, the environment is affected by CVE-2001-1556.
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 data1.3.312.0.49
Upgrade to a patched Apache version or implement log sanitization/filtering to escape control characters before logging.
Fix this in HTTP Server
Scoped from the published advisory
- Consultation2.0 h
- Implementation3.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,272.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2001-1556 — 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-2001-1556 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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