CVE-2011-4096
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 idnsGrokReply function in Squid before 3.1.16 does not properly free memory, which allows remote attackers to cause a denial of service (daemon abort) via a DNS reply containing a CNAME record that references another CNAME record that contains an empty A record.
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 confidenceSquid proxy server before version 3.1.16 contains a memory leak in the idnsGrokReply function when processing DNS responses. Specifically, when a CNAME record chains to another CNAME record containing an empty A record, the function fails to properly free allocated memory, leading to memory exhaustion and daemon 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<= 3.1.15= 3.0= 3.0.stable1= 3.0.stable2= 3.0.stable3= 3.0.stable4= 3.0.stable5= 3.0.stable6= 3.0.stable7= 3.0.stable8= 3.0.stable9= 3.0.stable10CVSS 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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Identify Squid versionRun 'squid -v' or 'squid -V' to display the installed Squid version numberAffected if The version displayed is 3.0.x through 3.0.stable10, or any version 3.1.15 or lower, or 3.1.x versions up to 3.1.15
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Confirm DNS processing is activeCheck the Squid configuration file (typically /etc/squid/squid.conf or /etc/squid3/squid.conf) for dns_children or DNS lookup directives. Verify Squid is configured to perform DNS resolution for client requests.Affected if DNS processing is enabled in the configuration, which is the default state for most Squid installations
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Verify CNAME chain handling is possibleConfirm that Squid is configured to allow DNS CNAME resolution. Look for 'dns_defnames on' or similar directives, or confirm the proxy is used for domains that may have CNAME records pointing to other CNAMEs.Affected if Squid processes DNS responses containing CNAME chains, which is typical behavior when forwarding requests to external domains
A system is affected if it runs any Squid version listed in the affected ranges (3.0.x through 3.0.stable10, or 3.1.x versions 3.1.15 or lower) and has DNS resolution enabled, as the memory leak triggers during CNAME-to-CNAME chain processing with empty A records.
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 Squid to version 3.1.16 or later to patch the memory management flaw in DNS response handling.
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2011-4096 — 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-2011-4096 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
- No weaponised exploit code, or anything meant to cause harm
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