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Debian LinuxOperating system · Debian

CVE-2019-12519

CRITICAL · 9.8 CVSS v3.1 Published 2020-04-15
Fix available
A fix is available. Upgrade to after 5.0.1 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 the tag esi:when when ESI is enabled, Squid calls ESIExpression::Evaluate. This function uses a fixed stack buffer to hold the expression while it's being evaluated. When processing the expression, it could either evaluate the top of the stack, or add a new member to the stack. When adding a new member, there is no check to ensure that the stack won't overflow.

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

Stack buffer overflow in Squid's ESIExpression::Evaluate function when processing esi:when tags with ESI enabled. The function uses a fixed-size stack buffer without bounds checking when adding new expression members, allowing overflow and potential remote code execution.

MitigationUpgrade to Squid 4.8 or later which contains the patched bounds checking, or if upgrading is not feasible, disable ESI processing in the Squid configuration to eliminate the attack surface.

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= 19.10= 20.04
SquidApplication
Affected:>= 3.0, <= 3.5.28>= 4.0, <= 4.10>= 5.0, <= 5.0.1
LeapOperating system
Affected:= 15.1

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. Identify Squid version
    Run 'squid -v' or 'squid -V' to display the installed Squid version number
    Affected if Version is 3.0 through 3.5.28, 4.0 through 4.10, or 5.0 through 5.0.1 (vulnerable range)
  2. Locate Squid configuration file
    Find the squid.conf file (typically /etc/squid/squid.conf or /etc/squid3/squid.conf)
    Affected if Configuration file exists and ESI processing is enabled
  3. Check if ESI is enabled
    Search the squid.conf file for ESI-related directives. Look for lines containing 'esi:' or check if ESI processing is not explicitly disabled. The directive 'esi' by itself enables ESI support.
    Affected if ESI is enabled in the configuration (the vulnerability only triggers when ESI is active)
  4. Verify esi: when tag processing capability
    Confirm the Squid build supports ESI processing by examining the output of 'squid -v' for ESI-related features or by checking for the 'esi_feature' directive in the configuration
    Affected if Squid is compiled with ESI support and ESI is turned on in config

You are affected if your Squid version falls within 3.0-3.5.28, 4.0-4.10, or 5.0-5.0.1 AND ESI processing is enabled in your 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 5.0.1
Interim mitigation

Upgrade to Squid 4.8 or later which contains the patched bounds checking, or if upgrading is not feasible, disable ESI processing in the Squid configuration to eliminate the attack surface.

Recommended fix High confidence

Squid 4.11 or later (4.x series); Squid 3.5.29 (3.x series); Squid 5.0.2 or later (5.x series)

  1. 1. Identify the currently installed Squid version using: dpkg -l | grep squid or rpm -qa | grep squid
  2. 2. For Debian/Ubuntu: Run 'apt-get update && apt-get install squid' to get the latest available version in the distribution repositories
  3. 3. For Squid source installations: Download Squid 4.11 or later from www.squid-cache.org/Download/http-list.html
  4. 4. If building from source, ensure ESI support is enabled (--enable-esi flag) to match the vulnerable configuration
  5. 5. Restart the Squid service using: systemctl restart squid or service squid restart
  6. 6. Verify the new version is running: squid -v | grep version
Caveat Upgrading Squid may require configuration adjustments; ensure backup of squid.conf before upgrade; some ESI-related configuration options may have changed

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

Fix this in Debian Linux Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,930
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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-2019-12519 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