CVE-2026-73257Public exploitNetwork attack vector

Cross-user access via CL.TE request smuggling

Published Aug 20, 2026 · Updated Aug 20, 2026

HTTP request smuggling in Cesanta Mongoose before 7.22 allows remote attackers to access or modify resources in another user context via CL.TE desynchronization. In src/http.c, the mg_http_parse() and http_cb() paths accept requests that contain both Content-Length and Transfer-Encoding headers and then process the body as chunked instead of rejecting the conflicting framing. Exploitation requires Mongoose to sit behind a Content-Length-preferring reverse proxy, so front-end and back-end request boundaries diverge and a smuggled request can be attributed to the next client on the connection.

CVSS severity9.1
Critical
EPSS probability0.48%
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 Cesanta Mongoose before 7.22 allows remote attackers to access or modify resources in another user context via CL.TE desynchronization. In src/http.c, the mg_http_parse() and http_cb() paths accept requests that contain both Content-Length and Transfer-Encoding headers and then process the body as chunked instead of rejecting the conflicting framing. Exploitation requires Mongoose to sit behind a Content-Length-preferring reverse proxy, so front-end and back-end request boundaries diverge and a smuggled request can be attributed to the next client on the connection.

The record

CVE
CVE-2026-73257
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
Cesanta
Product
Mongoose
Classifications
CWE-444, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 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.

  1. Affected versionversion=< 7.22

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cesanta · Mongooseversion=< 7.22

Published CVSS scores

9.1GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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.

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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 exploitPublished

Weakness, pattern, technique

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

Public exploit references

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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