FedoraOperating system · Fedoraproject
CVE-2021-28116
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 · uneditedSquid through 4.14 and 5.x through 5.0.5, in some configurations, allows information disclosure because of an out-of-bounds read in WCCP protocol data. This can be leveraged as part of a chain for remote code execution as nobody.
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 confidenceSquid proxy server versions 4.14 and earlier and 5.x through 5.0.5 contain an out-of-bounds read vulnerability in the WCCP (Web Cache Coordination Protocol) protocol handler. This memory safety flaw allows information disclosure and can be chained with other vulnerabilities to achieve remote code execution as the unprivileged 'nobody' user.
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
FedoraOperating system
= 33= 34
Debian LinuxOperating system
= 10.0= 11.0<= 4.14>= 5.0, <= 5.0.5CVSS 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
- Low
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/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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Identify Squid installation and versionRun 'squid -v' or check the package manager (e.g., 'rpm -q squid' on Fedora, 'dpkg -l squid' on Debian). The output displays the installed version number.Affected if The version displayed is 4.14 or earlier, or falls between 5.0 and 5.0.5 inclusive.
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Locate the Squid configuration fileThe configuration is typically at /etc/squid/squid.conf or /etc/squid.conf. Use 'squid -k parse 2>&1 | head' to confirm the active config path.Affected if A configuration file exists and is readable for the next step.
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Check if WCCP is enabledSearch the Squid configuration file for any WCCP-related directives: grep -i wccp /etc/squid/squid.conf (or /etc/squid.conf). Look for keywords such as wccp2_router, wccp2_service, wccp_address, wccp_version, or any line containing 'wccp'.Affected if Any WCCP directives are present and uncommented in the configuration file.
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Verify WCCP service is runningCheck for active WCCP-related processes or ports: ps aux | grep squid combined with netstat -tlnp | grep (port) or review system logs for WCCP initialization messages.Affected if WCCP services or listeners are actively running or bound to network interfaces.
You are affected if Squid version is 4.14 or earlier, or between 5.0 and 5.0.5, AND WCCP functionality is configured and enabled in your Squid deployment.
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 to Squid version 4.15 or 5.1 or later, or disable WCCP functionality if not required in the deployment.
Fix this in Fedora
Scoped from the published advisory
- Consultation3.0 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 $3,408.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-28116 — 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-2021-28116 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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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- 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
- No spam, self-promotion, credentials, or personal data