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Debian LinuxOperating system · Debian

CVE-2019-12524

CRITICAL · 9.8 CVSS v3.1 Published 2020-04-15
Fix available
A fix is available. Upgrade to after 4.7 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 · unedited
An issue was discovered in Squid through 4.7. When handling requests from users, Squid checks its rules to see if the request should be denied. Squid by default comes with rules to block access to the Cache Manager, which serves detailed server information meant for the maintainer. This rule is implemented via url_regex. The handler for url_regex rules URL decodes an incoming request. This allows an attacker to encode their URL to bypass the url_regex check, and gain access to the blocked resource.

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 confidence

Squid's url_regex access control handler decodes incoming request URLs before checking them against deny rules. Since the default rules blocking access to the Cache Manager use url_regex patterns that match decoded URLs, attackers can bypass these restrictions by sending URL-encoded requests (e.g., encoding characters in '/cachemgr.cgi') to access the protected Cache Manager interface.

MitigationUpgrade Squid to version 4.8 or later which contains the patch, or implement additional access control layers (e.g., IP-based restrictions, authentication) for the Cache Manager to defense-in-depth.

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
Debian LinuxOperating system
Affected:= 9.0= 10.0
Ubuntu LinuxOperating system
Affected:= 16.04= 18.04
SquidApplication
Affected:<= 4.7

CVSS 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
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Squid version
    Run 'squid -v' or 'squid -V' to display version information, or check the package manager (dpkg -l squid, rpm -qi squid)
    Affected if Squid version is 4.7 or earlier (versions 4.8 and later contain the fix)
  2. Verify Cache Manager is enabled
    Search squid.conf for 'cachemgr' entries or check for 'cgi-bin/cachemgr' in the configuration. Look for http_access rules containing 'cachemgr' or 'cache_manager'
    Affected if Cache Manager interface is accessible via http_access rules and no additional authentication or IP restriction is applied
  3. Identify url_regex ACLs blocking Cache Manager
    Examine squid.conf for 'url_regex' access control entries that match 'cachemgr' or '/cachemgr.cgi'. Use 'grep -i url_regex squid.conf' to find these patterns
    Affected if Deny rules using url_regex patterns are configured to block Cache Manager access (these rules are vulnerable to the bypass)
  4. Check for recent URL-encoded Cache Manager requests
    Review Squid access logs (typically in /var/log/squid/access.log) for requests to paths containing URL-encoded characters targeting the Cache Manager (e.g., '%2f', '%63%61%63%68%65%6d%67%72')
    Affected if URL-encoded requests to Cache Manager are present in logs, indicating exploitation attempts or successful bypass

You are affected if Squid version is 4.7 or earlier AND url_regex ACLs deny access to the Cache Manager without additional authentication or IP-based restrictions, as URL-encoded requests can bypass these rules.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Upgrade available Upgrade to a release after 4.7
Interim mitigation

Upgrade Squid to version 4.8 or later which contains the patch, or implement additional access control layers (e.g., IP-based restrictions, authentication) for the Cache Manager to defense-in-depth.

Recommended fix Moderate confidence

Upgrade to a Squid version greater than 4.7 (such as 4.8 or later stable release)

  1. 1. Identify the current Squid version installed by running: squid -v or squid -V
  2. 2. Update the package repository metadata: apt-get update (for Debian/Ubuntu)
  3. 3. Upgrade Squid to the latest available version: apt-get install squid
  4. 4. Verify the new version is installed: squid -v
  5. 5. Review Squid configuration files (typically /etc/squid/squid.conf) to ensure no custom url_regex rules that may have been workarounds are still needed
  6. 6. Test Squid service starts correctly: systemctl start squid or systemctl restart squid
  7. 7. Verify the service is running: systemctl status squid
Caveat Minor: Custom url_regex rules configured as a workaround may need cleanup; ensure configuration testing before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Debian Linux Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,800
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2019-12524 in production — separate from our analysis above.

No notes yet

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What this is

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.

What belongs here
  • 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