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Public proof of conceptFix available

CVE-2026-73257

A public proof of concept exists; no exploitation attested.

  • Published2026-08-20
  • Fixed in7.22
  • WeaknessCWE-444

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The cl_count and te_count checks in the mg_http_parse() and http_cb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. This issue is fixed in version 7.22.

Timeline

dates in UTC
  1. 2026-08-2018:16CVE publishedNVD

Versions per branch

NVD
Cesanta mongoose
BranchAffectedFixed in
7.22< 7.227.22

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As GitHub_M, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • cesanta mongoose
    Affected
    • = < 7.22no fix stated

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-08-20

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • mongooseUbuntu:26.10all versions · no fixed version listed
  • mongooseDebian:14all versions · fixed in 7.22+ds-1

Vendor advisories

  • CVE-2026-73257 Red Hat Product Security

    mongoose: Mongoose: Content-Length + Transfer-Encoding coexistence enables request smuggling

Full record on NVD

Fix

  1. Update Cesanta mongoose to 7.22

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • NVDCVE recordread 2026-10-23
  • CISA-ADPSSVC decisionpoc2026-08-20
  • CNACVSS 3.19.1known since 2026-10-23
  • CNAweakness (CWE)CWE-444known since 2026-10-23
  • FIRST EPSSEPSS score0.7 %2026-11-08
  • OSVaffected packages—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Published
2026-08-20
Last Modified
2026-10-18
NVD status
Analyzed

Frequently asked questions

What is CVE-2026-73257?

Mongoose is an embedded web server and network library. Priro to version 7.22, a remote unauthenticated attacker can send an HTTP request containing both Content-Length and Transfer-Encoding: chunked. The cl_count and te_count checks in the mg_http_parse() and http_cb() paths in src/http.c accept both headers and prioritize chunked encoding, while a Content-Length-preferring reverse proxy can use a different request boundary. This CL.TE desynchronization can inject requests that access or modify resources in another user context. This issue is fixed in version 7.22.

Is CVE-2026-73257 actively exploited?

A proof-of-concept exploit exists for CVE-2026-73257, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-73257?

CVE-2026-73257 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

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