Authentication bypass via unchecked absolute-form root URLs
Published Mar 27, 2026 · Updated Mar 27, 2026
HTTP/1.1 request parsing in Varnish Cache before 8.0.1 allows remote attackers to poison caches or bypass authentication. For an absolute-form root URL, the parser preserves a non-origin-form req.url and forwards it unchecked to backends that accept absolute-form URIs. Exploitation requires such a backend and an unvalidated req.url path; requests for non-root paths are outside the reported attack surface.
Summary
What happened
HTTP/1.1 request parsing in Varnish Cache before 8.0.1 allows remote attackers to poison caches or bypass authentication. For an absolute-form root URL, the parser preserves a non-origin-form req.url and forwards it unchecked to backends that accept absolute-form URIs. Exploitation requires such a backend and an unvalidated req.url path; requests for non-root paths are outside the reported attack surface.
The record
- CVE
- CVE-2026-34475
- Published
- Mar 27, 2026
- Updated
- Mar 27, 2026
- Vendor
- Varnish Software
- Product
- Varnish Cache
- Classifications
- CWE-180, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Mar 27, 2026CVE publishedPublication date reported by the CVE source.
- Mar 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <6.0.17 LTS
- Affected versionversion=7.0.0 <8.0.1
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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