CVE-2026-66731

HIGHPre-NVD 7.57.5
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

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, GitHub Security Advisory, a secondary CVSS source
Trending — 3 sources updated this weekElevated
7.5EG
EchelonGraph verdictPlan mitigationRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.8%CVSS: 7.5Exploit: No code on recordExposed services: Not assessed

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

The CVE record's CNA (VulnCheck) lists boazsegev facil.io versions 0.7.5 up to and including 0.7.6 as affected. No release containing a fix is confirmed on record.

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
7.5HIGHmedium confidence
EG Risk
65
EG Risk 65/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity75% × 45%
Impact severity (EG Severity): CVSS 7.5 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
EPSS PROB
0.8%
EPSS %ILE
55th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (7.5): severity, escalated by confirmed exploitation. This CVE's 7.5 is its impact severity (EG Severity), not escalated.

EG Severity
7.5 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.8% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-19). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.

Exploitation public PoC (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

July 27, 2026

Last Modified

July 31, 2026

Advisory Details (2)

Auto-updated Jul 27, 2026
No fix on record yet.
Web page

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
Web page

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 12× in last 7d / 55× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 248 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 148 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-20 09:05 UTCEG score recompute
  2. 2026-10-20 09:04 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  3. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  4. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  5. 2026-10-18 03:20 UTCEG score recompute
  6. 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  7. 2026-10-16 16:43 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  8. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  9. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.8% · 55th percentile
  10. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  11. 2026-10-13 10:52 UTCEG score recompute
  12. 2026-10-13 10:52 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  13. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  14. 2026-10-12 15:46 UTCEG score recompute
  15. 2026-10-11 19:31 UTCEG score recompute
  16. 2026-10-11 16:46 UTCEG score recompute
  17. 2026-10-11 14:07 UTCEG score recompute
  18. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  19. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  20. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  21. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  22. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  23. 2026-10-07 02:27 UTCEG score recompute
  24. 2026-10-07 02:27 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  25. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.8% · 54th percentile
Show 75 more
  1. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  2. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  3. 2026-10-04 07:18 UTCEG score recompute
  4. 2026-10-04 07:18 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  5. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  6. 2026-10-02 18:27 UTCEG score recompute
  7. 2026-10-02 18:27 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  8. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  9. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  10. 2026-10-01 15:45 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  11. 2026-10-01 03:52 UTCEG score recompute
  12. 2026-10-01 03:52 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  13. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  14. 2026-09-29 07:53 UTCEG score recompute
  15. 2026-09-29 07:53 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  16. 2026-09-28 13:52 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  17. 2026-09-28 03:34 UTCEG score recompute
  18. 2026-09-28 03:33 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  19. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  20. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.8% · 54th percentile
  21. 2026-09-25 06:52 UTCEG score recompute
  22. 2026-09-25 06:52 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  23. 2026-09-24 09:49 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  24. 2026-09-23 22:02 UTCEG score recompute
  25. 2026-09-23 22:02 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  26. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  27. 2026-09-23 09:35 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  28. 2026-09-22 21:48 UTCEG score recompute
  29. 2026-09-22 21:48 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  30. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  31. 2026-09-20 00:55 UTCEG score recompute
  32. 2026-09-20 00:55 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  33. 2026-09-19 08:17 UTCEG score recompute
  34. 2026-09-19 08:17 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  35. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  36. 2026-09-18 18:53 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  37. 2026-09-18 02:23 UTCEG score recompute
  38. 2026-09-18 02:23 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  39. 2026-09-17 01:46 UTCEG score recompute
  40. 2026-09-17 01:46 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  41. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  42. 2026-09-16 06:16 UTCEG score recompute
  43. 2026-09-16 06:16 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  44. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  45. 2026-09-15 09:08 UTCEG score recompute
  46. 2026-09-15 09:08 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  47. 2026-09-14 08:41 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  48. 2026-09-13 20:55 UTCEG score recompute
  49. 2026-09-13 20:55 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  50. 2026-09-13 08:23 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  51. 2026-09-12 20:37 UTCEG score recompute
  52. 2026-09-12 20:37 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  53. 2026-09-12 08:49 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  54. 2026-09-11 20:26 UTCEG score recompute
  55. 2026-09-11 20:26 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  56. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  57. 2026-09-11 09:37 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  58. 2026-09-11 08:34 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  59. 2026-09-10 20:47 UTCEG score recompute
  60. 2026-09-10 20:47 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  61. 2026-09-10 08:14 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  62. 2026-09-09 08:19 UTCEG score recompute
  63. 2026-09-09 08:19 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  64. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  65. 2026-09-07 21:03 UTCEG score recompute
  66. 2026-09-07 21:03 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  67. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  68. 2026-09-06 23:28 UTCEG score recompute
  69. 2026-09-06 23:28 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  70. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  71. 2026-09-06 07:41 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  72. 2026-09-05 19:15 UTCEG score recompute
  73. 2026-09-05 19:15 UTCGHSA enrichmentGHSA-vg6c-748h-g68q · GitHub severity HIGH · GitHub CVSS 7.5
  74. 2026-09-05 15:31 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  75. 2026-09-05 05:45 UTCEG score recompute

Frequently asked(5)

What is CVE-2026-66731?
CVE-2026-66731 is a high-severity vulnerability; its CVE record was 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 made public?
CVE-2026-66731 was made public on July 24, 2026: that is the date its CVE record's CNA, VulnCheck, gives for when the vulnerability was made public. The CVE record itself was published on July 27, 2026. EchelonGraph's copy of the record carries a last-modified date of July 31, 2026; the record at its source may have been updated since.
Is CVE-2026-66731 actively exploited?
CVE-2026-66731 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.8% probability of exploitation in the next 30 days (55th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-66731?
CVE-2026-66731 has a CVSS base score of 7.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-66731?
No fix for CVE-2026-66731 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The CVE record's CNA (VulnCheck) lists boazsegev facil.io versions 0.7.5 up to and including 0.7.6 as affected. No release containing a fix is confirmed on record. The vendor advisories EchelonGraph has for CVE-2026-66731 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-66731

Explore →

Is Your Infrastructure Affected by CVE-2026-66731?

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