CVE-2025-4600Network attack vector

Request smuggling via oversized chunk-body parsing

Published May 16, 2025 · Updated Sep 8, 2025

HTTP request smuggling in Google Cloud Classic Application Load Balancer before April 26, 2025 allows remote attackers to alter backend requests. Its chunked-body parser accepts oversized chunks and ignores trailing bytes that an upstream server can reinterpret as a line terminator. Exploitation requires a crafted chunked request and differing backend message-boundary parsing, allowing hidden bytes to become a separate request.

CVSS severity8.7
High
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in Google Cloud Classic Application Load Balancer before April 26, 2025 allows remote attackers to alter backend requests. Its chunked-body parser accepts oversized chunks and ignores trailing bytes that an upstream server can reinterpret as a line terminator. Exploitation requires a crafted chunked request and differing backend message-boundary parsing, allowing hidden bytes to become a separate request.

The record

CVE
CVE-2025-4600
Published
May 16, 2025
Updated
Sep 8, 2025
Vendor
Google Cloud
Product
Classic Application Load Balancer
Classifications
CWE-444, CAPEC-33, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 16, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 8, 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=0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Google Cloud · Classic Application Load Balancerversion=0

Published CVSS scores

8.7Google Inc.CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:L/SA:L

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.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 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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