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CriticalVulnerabilityupdated 27 Oct 2026, 12:18 UTC

Squid proxy flaw lets remote attackers bypass safeguards and leak data

Squid is a widely used proxy server that sits between users and the internet. A flaw in it could let an outside attacker get around its protections and see information they should not have.

Official source
SeverityCriticalVulnerability
Being exploited?UnclearNo reports either way yet
Fix available?UnclearNo fixed version published in the sources yet
How sure is this?Official sourceBacked by an official source

What happened

A critical vulnerability in Squid allows a remote, unauthenticated attacker to bypass security mechanisms and disclose information. The source does not specify the affected component or exact flaw.

Why it is dangerous: Attackers could reach data passing through or stored on affected Squid servers, and organizations that expose Squid to the internet or rely on it for access control are at highest risk.

Are you affected?

You are affected if you run a Squid proxy server in a version listed as vulnerable, but the affected versions are not stated in the material.

What to do

  1. Check whether your organization runs Squid and identify all instances
  2. Check the official Squid security advisory for the fixed version and update to it
  3. Restrict access to Squid to trusted networks until the update is applied
  4. Review Squid logs for unusual requests

Timeline

  1. 27 Oct 2026, 12:16 UTC
    Publicly disclosed
  2. 27 Oct 2026, 12:16 UTC
    Reported by CERT-Bund (BSI) · CERT-Bund (BSI)
  3. 27 Oct 2026, 12:18 UTC
    Picked up by Zero Radar

Sources 1 report, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
ZR-9c4c03a0
Disclosed
27 Oct 2026, 12:16 UTC
On Zero Radar
27 Oct 2026, 12:18 UTC (2 min after disclosure)
Last change
27 Oct 2026, 12:18 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

Squid proxy flaw lets remote attackers bypass safeguards and leak data · Zero Radar