CVE-2026-73257

CRITICALPre-NVD 9.19.1—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.1 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.7% (50th percentile of EPSS-scored CVEs). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Elevated
9.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.7%CVSS: 9.1Exploit: Elevated riskExposed services: Not assessed

A fix is available — apply it.

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.

CVSS v3
9.1
EG Score
9.1CRITICALmedium confidence
EG Risk
72
EG Risk 72/100CISA SSVC

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity91% × 45%
Exploitation40% × 40%
Automatability100% × 15%
CISA SSVC: Track at low, Track* at medium and Attend at high mission impact.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.7%
EPSS %ILE
50th
KEV
Not listed

CISA SSVCTrack at low, Track* at medium and Attend at high mission impact.

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table

Published

August 20, 2026

Last Modified

September 29, 2026

Advisory Details (4)

Auto-updated Sep 15, 2026
🔬 Proof of concept available. Patch available. Sources: github_pr, github_release, github, github_commit.
githubMentions a patch (unverified)🟡 PoC Available

Content-Length + Transfer-Encoding coexistence enables request smuggling · Advisory · cesanta/mongoose · GitHub

https://github.com/cesanta/mongoose/security/advisories/GHSA-5wfq-r6mr-wqp6
github_release Patch Available

Mongoose 7.22

Patch available: cesanta/mongoose 7.22

https://github.com/cesanta/mongoose/releases/tag/7.22
github_pr Patch Available

assorted patches

Patch available: cesanta/mongoose 7.22 (PR #3611 merged 2026-06-23)

https://github.com/cesanta/mongoose/pull/3611
github_commit Patch Available

commit a9df523f76f4 (cesanta/mongoose)

Patch available: cesanta/mongoose 7.22 (contains commit a9df523f76f4)

https://github.com/cesanta/mongoose/commit/a9df523f76f43a38bd53b4232b9cfd4c16869e71

Affected Packages

(1 across 1 ecosystem)
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
mongoose7.21+ds-1, 7.21+ds-1~bpo13+1, 7.21+ds-2, 7.22+ds-1~bpo13+1
  • every version up to 7.22+ds-1: fixed in 7.22+ds-1
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 11× in last 7d / 49× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-10-10 20:00 UTCEPSS rescore
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  22. 2026-09-27 16:07 UTCEG score recompute
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  1. 2026-09-24 16:56 UTCEG score recompute
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  31. 2026-09-06 13:48 UTCEPSS rescore
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  46. 2026-08-30 01:57 UTCEG score recompute
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  56. 2026-08-24 17:38 UTCEG score recompute
  57. 2026-08-24 09:32 UTCEG score recompute
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  60. 2026-08-22 00:43 UTCEG score recompute
  61. 2026-08-21 23:49 UTCEPSS rescore
  62. 2026-08-20 20:20 UTCEG score recompute
  63. 2026-08-20 19:37 UTCEG score recompute
  64. 2026-08-20 18:17 UTCEG score recompute
  65. 2026-08-20 17:46 UTCEG score recompute
  66. 2026-08-20 17:46 UTCMITRE cvelistV5first tracked

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-73257?
CVE-2026-73257 is a critical vulnerability published on August 20, 2026. 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 clcount and tecount checks in the mghttpparse() and http_cb() paths in src/http.c accept both…
When was CVE-2026-73257 disclosed?
CVE-2026-73257 was first published on August 20, 2026, with the most recent update on September 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-73257 actively exploited?
CVE-2026-73257 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.7% probability of exploitation in the next 30 days (50th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-73257?
CVE-2026-73257 has a CVSS base score of 9.1 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-73257?
A fix for CVE-2026-73257 is available: update to the fixed version the vendor names in its advisory.

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