PHPApplication
CVE-2015-6838
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 xsl_ext_function_php function in ext/xsl/xsltprocessor.c in PHP before 5.4.45, 5.5.x before 5.5.29, and 5.6.x before 5.6.13, when libxml2 before 2.9.2 is used, does not consider the possibility of a NULL valuePop return value before proceeding with a free operation after the principal argument loop, which allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a crafted XML document, a different vulnerability than CVE-2015-6837.
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 xsl_ext_function_php in PHP's XSL extension (ext/xsl/xsltprocessor.c) fails to validate NULL return values before executing free operations in the principal argument loop when used with libxml2 before 2.9.2. This allows remote attackers to trigger a NULL pointer dereference and crash the PHP application by supplying a specially crafted XML document.
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
PHPApplication
= 5.6.0= 5.6.1= 5.6.2= 5.6.3= 5.6.4= 5.6.5= 5.6.6= 5.6.7= 5.6.8= 5.6.9= 5.6.10= 5.6.11<= 2.9.1CVSS 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:3.0/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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Check installed PHP versionRun `php -v` and note the version number in the output (e.g., PHP 5.6.8)Affected if PHP version is 5.6.0, 5.6.1, 5.6.2, 5.6.3, 5.6.4, 5.6.5, 5.6.6, 5.6.7, 5.6.8, 5.6.9, 5.6.10, or 5.6.11
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Check installed libxml2 versionRun `php -i` and locate the libxml section, or run `php -r 'echo LIBXML_DOTTED_VERSION;'` to get the exact libxml2 versionAffected if libxml2 version is 2.9.1 or lower
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Verify XSL extension is loadedRun `php -m` and check for 'xsl' in the module list, or run `php -i | grep -i xsl` to confirm the XSL extension is enabledAffected if The XSL extension appears in the loaded modules list (vulnerability only applies when XSL is in use)
You are affected if your PHP version is 5.6.0-5.6.11, your libxml2 version is 2.9.1 or lower, and the XSL extension is loaded and processing untrusted XML/XSL documents.
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 PHP to version 5.4.45 or higher (5.5.29+/5.6.13+), or preferably to PHP 7.x, and ensure libxml2 is updated to 2.9.2 or later to eliminate the NULL pointer dereference in the XSL extension.
Fix this in PHP
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 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 $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2015-6838 — 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-2015-6838 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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