dbcve.org
Ubuntu LinuxOperating system · Canonical

CVE-2019-12526

CRITICAL · 9.8 CVSS v3.1 Published 2019-11-26
Fix available
A fix is available. Upgrade to after 4.8 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 before 4.9. URN response handling in Squid suffers from a heap-based buffer overflow. When receiving data from a remote server in response to an URN request, Squid fails to ensure that the response can fit within the buffer. This leads to attacker controlled data overflowing in the heap.

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

A heap-based buffer overflow exists in Squid's URN response handling where the server fails to validate that incoming response data from a remote server fits within the allocated buffer before copying, allowing attacker-controlled data to overflow onto the heap.

MitigationUpgrade Squid to version 4.9 or later which contains the bounds checking fix for URN response handling. This is a critical (CVSS 9.8) vulnerability exploitable by malicious upstream servers.

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
Ubuntu LinuxOperating system
Affected:= 16.04= 18.04= 19.04= 19.10
FedoraOperating system
Affected:= 30= 31
Debian LinuxOperating system
Affected:= 8.0= 9.0= 10.0
SquidApplication
Affected:>= 3.0, <= 3.5.28>= 4.0, <= 4.8
LeapOperating system
Affected:= 15.0

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. Find installed Squid version
    Run 'squid -v' or 'squid -V' to see the version string. On Debian/Ubuntu use 'dpkg -l | grep squid'. On Red Hat/Fedora use 'rpm -q squid'. On openSUSE use 'rpm -q squid'.
    Affected if Version is 3.0 through 3.5.28, or 4.0 through 4.8 (versions before 4.9)
  2. Locate Squid configuration file
    Common locations are /etc/squid/squid.conf, /etc/squid3/squid.conf, or /etc/squid/squid.conf.default. Use 'squid -k parse 2>&1 | head -20' to see which config file is being used.
    Affected if Configuration file exists (required for next check)
  3. Check if URN support is enabled
    Search the squid.conf file for URN-related directives: grep -i 'urn' /etc/squid/squid.conf. Look for 'urn:' URL prefixes in any cache_peer or redirector configuration, or any 'urn' directive.
    Affected if URN module or 'urn:' protocol handling is explicitly configured or enabled in squid.conf
  4. Verify URN is actively used
    Check for any access rules or URL rewrites that direct traffic through URN handling. Review any custom redirector or helper programs that may invoke URN functionality.
    Affected if Squid is configured to process URN requests or forward requests to URN-enabled peers

You are affected if Squid version is 3.0-3.5.28 or 4.0-4.8 AND the URN protocol module or 'urn:' URL handling is enabled in your Squid configuration.

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 4.8
Interim mitigation

Upgrade Squid to version 4.9 or later which contains the bounds checking fix for URN response handling. This is a critical (CVSS 9.8) vulnerability exploitable by malicious upstream servers.

Recommended fix High confidence

Squid 4.9 or later

  1. Back up your current Squid configuration file (typically /etc/squid/squid.conf)
  2. Update your system's package repository to fetch the latest package lists
  3. Upgrade the Squid package using your distribution's package manager (e.g., apt-get update && apt-get install squid for Debian/Ubuntu, dnf upgrade squid for Fedora, zypper update squid for openSUSE)
  4. Verify the installed Squid version is 4.9 or later using: squid -v
  5. Restore your Squid configuration if needed and test the configuration: squid -k parse
  6. Restart the Squid service to apply the update: systemctl restart squid
Caveat Review the Squid 4.9 release notes for any configuration changes or feature deprecations that may affect your setup

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

Fix this in Ubuntu Linux Scoped from the published advisory
  • Consultation1.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
6.0 hours of engineering $1,040
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Scan for this in your stack

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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-2019-12526 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