CVE-2017-12963
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 · uneditedThere is an illegal address access in Sass::Eval::operator() in eval.cpp of LibSass 3.4.5, leading to a remote denial of service attack. NOTE: this is similar to CVE-2017-11555 but remains exploitable after the vendor's CVE-2017-11555 fix (available from GitHub after 2017-07-24).
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 · moderate confidenceLibSass 3.4.5 contains an illegal address access vulnerability in the Sass::Eval::operator() function in eval.cpp. This memory safety issue allows remote attackers to cause a denial of service by providing specially crafted Sass input that triggers the illegal memory access. The vulnerability is distinct from but similar to CVE-2017-11555, and the prior CVE's fix did not fully remediate this issue.
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= 3.4.5CVSS 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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Identify LibSass library versionRun 'sassc --version' or check the shared library version (libsass.so/lib/libsass.dylib) using 'ldd' on Linux or 'otool -L' on macOS, or inspect the binary/version info of the application embedding LibSassAffected if The reported version is exactly 3.4.5 or falls within the 3.4.x branch without the complete fix
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Determine if applications process Sass inputAudit web servers, build pipelines, or applications that use LibSass for compiling Sass stylesheets; check configuration files and dependencies (package.json, Gemfile, or similar) for LibSass bindings such as node-sass, sassc-ruby, or phpsassAffected if Any application or service uses LibSass to compile Sass input from users or external sources without input validation
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Inspect the eval.cpp componentIf the LibSass source is present, verify the file eval.cpp contains the vulnerable Sass::Eval::operator() function implementation; check for presence of the incomplete fix from prior CVE-2017-11555 by reviewing commit history or patch statusAffected if The eval.cpp file in use contains the unpatched version of the operator() function that was not fully remediated after CVE-2017-11555
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Review runtime environment for untrusted Sass inputExamine web application endpoints, CI/CD pipelines, or APIs that accept Sass content and pass it to LibSass for compilation; check for any network-exposed Sass compilation featuresAffected if The environment allows untrusted or attacker-controlled Sass input to be processed by LibSass without sanitization
A system is affected if it runs LibSass version 3.4.5 and processes Sass input from untrusted sources through the vulnerable eval.cpp component.
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 LibSass to a version beyond 3.4.5 that includes the complete fix for this vulnerability, and ensure all applications using LibSass are updated to use the patched library version.
- Consultation2.0 h
- Implementation4.0 h
- Testing6.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2017-12963 — 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-2017-12963 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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