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VulnerabilityPublished

CVE-2026-34475: Varnish Cache · Incorrect Behavior Order: Validate Before Canonicalize

Affects Varnish CacheSource CVE Database V5

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Not known to be exploited · CVSS 5.4 Medium : upgrade to 8.0.1 or 6.0.17 LTS when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
5.4Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.2% chance of exploitation in 30 days – higher than 11% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 8.0.1, 6.0.17 LTS
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 27 Mar 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade Varnish Cache to 8.0.1 or 6.0.17 LTS.

Affected software

ProductAffectedFixed in
varnish-softwareVarnish CacheAffected
  • >=7.0.0 <8.0.1
  • =0
Fixed in
  • 8.0.1
  • 6.0.17 LTS

AI-suggested

Organizations should upgrade Varnish Cache to version 8.0.1 or later and Varnish Enterprise to 6.0.16r12 or later, where this vulnerability is fixed. If immediate patching is not feasible, administrators should implement strict input validation and URL normalization at the web application firewall (WAF) or reverse proxy level to ensure URLs are properly canonicalized before validation. Monitoring and logging of unusual or malformed requests targeting the root path '/' should be enhanced to detect potential exploitation attempts. Additionally, review and tighten cache key generation logic to prevent unauthorized cache entries. Employ network segmentation and access controls to limit exposure of Varnish Cache instances to untrusted networks. Regularly audit and update security policies related to caching infrastructure. Finally, stay informed about any emerging exploits or patches related to this CVE.

Description

Varnish Cache before 8.0.1 and Varnish Enterprise before 6.0.16r12, in certain unchecked req.url scenarios, mishandle URLs with a path of / for HTTP/1.1, potentially leading to cache poisoning or authentication bypass.

References

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