CVE-2026-66731

HIGHPre-NVD 7.57.5—
EchelonGraph scoreMEDIUM confidence

Score 7.5 from GitHub Security Advisory (severity: HIGH) published 2026-07-27. a secondary CVSS source baseline 7.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
7.5EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 7.5Exploit: Elevated riskExposed: 0

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

facil.io 0.7.5 through 0.7.6 contains a denial-of-service vulnerability in the HTTP/1.1 chunked transfer encoding parser that allows unauthenticated remote attackers to crash the server by sending a negative chunk size value. Attackers can send a single POST request with a Transfer-Encoding: chunked header containing a leading minus sign in the chunk size field, causing the parser in http1_parser.h to compute a large positive integer from the negated value, corrupting internal state and moving the read pointer into unmapped memory resulting in a fault.

CVSS v3
7.5
EG Score
7.5(medium)
EG Risk
65(Attend)
EG Risk 65/100SSVC: 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
Severity75% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
1%
EPSS %ILE
46%
KEV
Not listed

Published

July 27, 2026

Last Modified

July 31, 2026

Advisory Details (2)

Auto-updated Jul 27, 2026
🔬 Proof of concept available. No patch confirmed yet.
generic

facil.io 0.7.5 - 0.7.6 HTTP/1.1 Chunked Transfer Encoding Parser Crash DoS | Advisories | VulnCheck

https://www.vulncheck.com/advisories/facil-io-http-chunked-transfer-encoding-parser-crash-dos
generic🟡 PoC Available

GitHub - theopaid/Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-in-facil.io-leading-to-Server-Crash: Security Advisory: Negative Chunk-Size Parsing Causes Memory Corruption in facil.io · GitHub

https://github.com/theopaid/Negative-Chunk-Size-Parsing-Causes-Memory-Corruption-in-facil.io-leading-to-Server-Crash

Vendor Advisories for CVE-2026-66731(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 21× in last 7d / 113× 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.

Showing the most recent 100 of 133 total refreshes for this CVE.

  1. 2026-08-30 01:22 UTCEPSS rescore
  2. 2026-08-29 23:52 UTCEG score recompute
  3. 2026-08-29 23:52 UTCGHSA enrichment
  4. 2026-08-28 21:42 UTCEPSS rescore
  5. 2026-08-27 21:29 UTCEG score recompute
  6. 2026-08-27 21:29 UTCGHSA enrichment
  7. 2026-08-27 09:43 UTCGHSA enrichment
  8. 2026-08-26 20:19 UTCEG score recompute
  9. 2026-08-26 20:19 UTCGHSA enrichment
  10. 2026-08-26 14:47 UTCEPSS rescore
  11. 2026-08-26 08:32 UTCGHSA enrichment
  12. 2026-08-25 20:46 UTCEG score recompute
  13. 2026-08-25 20:46 UTCGHSA enrichment
  14. 2026-08-25 13:49 UTCEPSS rescore
  15. 2026-08-25 08:45 UTCGHSA enrichment
  16. 2026-08-24 20:59 UTCEG score recompute
  17. 2026-08-24 20:59 UTCGHSA enrichment
  18. 2026-08-24 09:12 UTCGHSA enrichment
  19. 2026-08-23 21:25 UTCGHSA enrichment
  20. 2026-08-23 09:39 UTCEG score recompute
  21. 2026-08-23 09:39 UTCGHSA enrichment
  22. 2026-08-23 00:19 UTCEPSS rescore
  23. 2026-08-22 21:53 UTCGHSA enrichment
  24. 2026-08-22 10:06 UTCEG score recompute
  25. 2026-08-22 10:06 UTCGHSA enrichment
Show 75 more
  1. 2026-08-21 23:49 UTCEPSS rescore
  2. 2026-08-21 22:14 UTCGHSA enrichment
  3. 2026-08-21 10:26 UTCEG score recompute
  4. 2026-08-21 10:26 UTCGHSA enrichment
  5. 2026-08-20 22:56 UTCEPSS rescore
  6. 2026-08-20 22:39 UTCGHSA enrichment
  7. 2026-08-20 10:53 UTCGHSA enrichment
  8. 2026-08-19 23:07 UTCEG score recompute
  9. 2026-08-19 23:07 UTCGHSA enrichment
  10. 2026-08-19 17:04 UTCEPSS rescore
  11. 2026-08-19 11:19 UTCGHSA enrichment
  12. 2026-08-18 23:33 UTCEG score recompute
  13. 2026-08-18 23:33 UTCGHSA enrichment
  14. 2026-08-18 13:48 UTCEPSS rescore
  15. 2026-08-18 11:45 UTCGHSA enrichment
  16. 2026-08-17 23:58 UTCEG score recompute
  17. 2026-08-17 23:58 UTCGHSA enrichment
  18. 2026-08-17 13:47 UTCEPSS rescore
  19. 2026-08-17 12:11 UTCGHSA enrichment
  20. 2026-08-17 00:25 UTCEG score recompute
  21. 2026-08-17 00:25 UTCGHSA enrichment
  22. 2026-08-16 14:56 UTCEPSS rescore
  23. 2026-08-16 12:38 UTCEG score recompute
  24. 2026-08-16 12:38 UTCGHSA enrichment
  25. 2026-08-16 00:52 UTCGHSA enrichment
  26. 2026-08-15 13:06 UTCEG score recompute
  27. 2026-08-15 13:06 UTCGHSA enrichment
  28. 2026-08-15 01:30 UTCEPSS rescore
  29. 2026-08-15 01:19 UTCGHSA enrichment
  30. 2026-08-14 13:33 UTCGHSA enrichment
  31. 2026-08-14 01:47 UTCEG score recompute
  32. 2026-08-14 01:47 UTCGHSA enrichment
  33. 2026-08-13 22:00 UTCEPSS rescore
  34. 2026-08-13 14:00 UTCGHSA enrichment
  35. 2026-08-13 02:14 UTCGHSA enrichment
  36. 2026-08-12 14:28 UTCEG score recompute
  37. 2026-08-12 14:27 UTCGHSA enrichment
  38. 2026-08-12 13:51 UTCEPSS rescore
  39. 2026-08-12 02:39 UTCGHSA enrichment
  40. 2026-08-11 14:53 UTCEG score recompute
  41. 2026-08-11 14:53 UTCGHSA enrichment
  42. 2026-08-11 03:07 UTCEG score recompute
  43. 2026-08-11 03:07 UTCGHSA enrichment
  44. 2026-08-11 00:00 UTCEPSS rescore
  45. 2026-08-10 15:21 UTCGHSA enrichment
  46. 2026-08-10 03:35 UTCGHSA enrichment
  47. 2026-08-09 15:48 UTCEG score recompute
  48. 2026-08-09 15:48 UTCGHSA enrichment
  49. 2026-08-09 13:47 UTCEPSS rescore
  50. 2026-08-09 04:02 UTCEG score recompute
  51. 2026-08-09 04:02 UTCGHSA enrichment
  52. 2026-08-08 16:37 UTCEPSS rescore
  53. 2026-08-08 16:16 UTCGHSA enrichment
  54. 2026-08-08 04:29 UTCGHSA enrichment
  55. 2026-08-07 16:43 UTCEG score recompute
  56. 2026-08-07 16:43 UTCGHSA enrichment
  57. 2026-08-07 04:57 UTCGHSA enrichment
  58. 2026-08-06 17:11 UTCEG score recompute
  59. 2026-08-06 17:11 UTCGHSA enrichment
  60. 2026-08-06 13:47 UTCEPSS rescore
  61. 2026-08-06 05:24 UTCEG score recompute
  62. 2026-08-06 05:24 UTCGHSA enrichment
  63. 2026-08-05 19:17 UTCEPSS rescore
  64. 2026-08-05 19:17 UTCEPSS rescore
  65. 2026-08-05 17:38 UTCGHSA enrichment
  66. 2026-08-05 05:52 UTCGHSA enrichment
  67. 2026-08-04 18:05 UTCEG score recompute
  68. 2026-08-04 18:05 UTCGHSA enrichment
  69. 2026-08-04 15:10 UTCEPSS rescore
  70. 2026-08-04 10:39 UTCEPSS rescore
  71. 2026-08-04 05:58 UTCGHSA enrichment
  72. 2026-08-03 18:12 UTCEG score recompute
  73. 2026-08-03 18:12 UTCGHSA enrichment
  74. 2026-08-03 10:36 UTCEPSS rescore
  75. 2026-08-03 06:25 UTCGHSA enrichment

Frequently asked(5)

What is CVE-2026-66731?
CVE-2026-66731 is a high vulnerability published on July 27, 2026. facil.io 0.7.5 through 0.7.6 contains a denial-of-service vulnerability in the HTTP/1.1 chunked transfer encoding parser that allows unauthenticated remote attackers to crash the server by sending a negative chunk size value. Attackers can send a single POST request with a Transfer-Encoding:…
When was CVE-2026-66731 disclosed?
CVE-2026-66731 was first published in the National Vulnerability Database on July 27, 2026, with the most recent update on July 31, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-66731 actively exploited?
CVE-2026-66731 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 54.2% of all scored CVEs.
What is the CVSS score of CVE-2026-66731?
CVE-2026-66731 has a CVSS v3 base score of 7.5 (NVD).
How do I remediate CVE-2026-66731?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-66731, 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

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