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: 0.5%, top 59% of all CVEs by exploit prediction. 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%CVSS: 9.1Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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
9.1(medium)
EG Risk
72(Attend)
EG Risk 72/100SSVC: Attend

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%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
41%
KEV
Not listed

Published

August 20, 2026

Last Modified

September 9, 2026

Advisory Details (4)

Auto-updated Sep 15, 2026
🔬 Proof of concept available. Patch available. Sources: github_pr, github_release, github, github_commit.
github Patch Available🟡 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 rangeFixed inDependents
mongoose7.21+ds-1, 7.21+ds-1~bpo13+1, 7.21+ds-2, 7.22+ds-1~bpo13+17.22+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 / 54× 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. 2026-09-19 18:29 UTCEG score recompute
  2. 2026-09-18 21:41 UTCEG score recompute
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-17 21:19 UTCEG score recompute
  5. 2026-09-16 14:29 UTCEG score recompute
  6. 2026-09-16 14:08 UTCEPSS rescore
  7. 2026-09-16 09:41 UTCEG score recompute
  8. 2026-09-16 05:15 UTCEPSS rescore
  9. 2026-09-15 03:52 UTCEG score recompute
  10. 2026-09-15 03:12 UTCEPSS rescore
  11. 2026-09-13 18:13 UTCEG score recompute
  12. 2026-09-12 17:52 UTCEG score recompute
  13. 2026-09-12 15:02 UTCEPSS rescore
  14. 2026-09-11 17:34 UTCEG score recompute
  15. 2026-09-11 14:53 UTCEPSS rescore
  16. 2026-09-11 12:58 UTCEG score recompute
  17. 2026-09-10 12:16 UTCEG score recompute
  18. 2026-09-10 09:35 UTCEPSS rescore
  19. 2026-09-09 01:57 UTCEG score recompute
  20. 2026-09-08 22:01 UTCEPSS rescore
  21. 2026-09-07 19:36 UTCEG score recompute
  22. 2026-09-06 16:28 UTCEG score recompute
  23. 2026-09-06 13:48 UTCEPSS rescore
  24. 2026-09-05 16:07 UTCEG score recompute
  25. 2026-09-04 15:19 UTCEG score recompute
Show 33 more
  1. 2026-09-04 07:12 UTCEG score recompute
  2. 2026-09-04 05:07 UTCEPSS rescore
  3. 2026-09-02 16:21 UTCEG score recompute
  4. 2026-09-02 14:12 UTCEPSS rescore
  5. 2026-09-01 15:24 UTCEG score recompute
  6. 2026-09-01 13:54 UTCEPSS rescore
  7. 2026-09-01 07:15 UTCEG score recompute
  8. 2026-09-01 04:40 UTCEPSS rescore
  9. 2026-09-01 04:40 UTCEPSS rescore
  10. 2026-08-30 22:16 UTCEG score recompute
  11. 2026-08-30 19:18 UTCEPSS rescore
  12. 2026-08-30 19:17 UTCEPSS rescore
  13. 2026-08-30 01:57 UTCEG score recompute
  14. 2026-08-30 01:22 UTCEPSS rescore
  15. 2026-08-29 01:28 UTCEG score recompute
  16. 2026-08-28 21:42 UTCEPSS rescore
  17. 2026-08-27 14:52 UTCEG score recompute
  18. 2026-08-27 14:25 UTCEPSS rescore
  19. 2026-08-26 18:26 UTCEG score recompute
  20. 2026-08-26 14:47 UTCEPSS rescore
  21. 2026-08-25 13:54 UTCEG score recompute
  22. 2026-08-25 13:49 UTCEPSS rescore
  23. 2026-08-24 17:38 UTCEG score recompute
  24. 2026-08-24 09:32 UTCEG score recompute
  25. 2026-08-23 01:04 UTCEG score recompute
  26. 2026-08-23 00:19 UTCEPSS rescore
  27. 2026-08-22 00:43 UTCEG score recompute
  28. 2026-08-21 23:49 UTCEPSS rescore
  29. 2026-08-20 20:20 UTCEG score recompute
  30. 2026-08-20 19:37 UTCEG score recompute
  31. 2026-08-20 18:17 UTCEG score recompute
  32. 2026-08-20 17:46 UTCEG score recompute
  33. 2026-08-20 17:46 UTCMITRE cvelistV5first tracked

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 in the National Vulnerability Database on August 20, 2026, with the most recent update on September 9, 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% probability of exploitation in the next 30 days, which ranks it in the top 59.1% of all scored CVEs.
What is the CVSS score of CVE-2026-73257?
CVE-2026-73257 has a CVSS v3 base score of 9.1 (NVD).
How do I remediate CVE-2026-73257?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-73257, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-73257

Explore →

Is Your Infrastructure Affected by CVE-2026-73257?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs