CVE-2025-30346Network attack vector

Request smuggling via retained rejected-request body

Published Mar 21, 2025 · Updated Apr 3, 2025

Client-side desynchronization in Varnish Cache 7.5.0 through 7.6.1 allows remote attackers to smuggle HTTP/1 requests. After rejecting a request with duplicate Host or Content-Length headers, the HTTP/1 parser leaves its body on the persistent connection and treats those bytes as the next request. Exploitation requires a front end that forwards the malformed request and can poison a downstream cache or bypass a downstream WAF configured not to inspect bodies.

CVSS severity4.8
Medium
EPSS probability0.30%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Client-side desynchronization in Varnish Cache 7.5.0 through 7.6.1 allows remote attackers to smuggle HTTP/1 requests. After rejecting a request with duplicate Host or Content-Length headers, the HTTP/1 parser leaves its body on the persistent connection and treats those bytes as the next request. Exploitation requires a front end that forwards the malformed request and can poison a downstream cache or bypass a downstream WAF configured not to inspect bodies.

The record

CVE
CVE-2025-30346
Published
Mar 21, 2025
Updated
Apr 3, 2025
Vendor
Varnish Software
Product
Varnish Cache
Classifications
CWE-444, CAPEC-33, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 21, 2025CVE publishedPublication date reported by the CVE source.
  2. Apr 3, 2025Record 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.

  1. Affected versionversion=7.5.0 <7.6.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Varnish Software · Varnish Cacheversion=7.5.0 <7.6.2

Published CVSS scores

5.4MITRECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N
4.8NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-444Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
CAPEC-33HTTP Request Smuggling
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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