CVE-2026-5388

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-08-23. A secondary CVSS source baseline 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.6%CVSS: 9.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript — for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw reintroduction through Markdown passthrough, or preserved // tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines.

CVSS v3
9.8
EG Score
9.8CRITICALmedium confidence
EG Risk
59
EG Risk 59/100CISA 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
Severity98% × 45%
Exploitation1% × 40%
Automatability100% × 15%
CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).
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
0.6%
EPSS %ILE
46th
KEV
Not listed

CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).

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

Exploitation none (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 23, 2026

Last Modified

August 26, 2026

Advisory Details (2)

Auto-updated Oct 8, 2026
Patch available. Sources: github.
generic

justhtml before 1.15.0 Multiple Security Issues | Advisories | VulnCheck

https://www.vulncheck.com/advisories/justhtml-before-multiple-security-issues
githubMentions a patch (unverified)

Multiple security fixes in justhtml 1.14.0 found by LLM · Advisory · EmilStenstrom/justhtml · GitHub

https://github.com/EmilStenstrom/justhtml/security/advisories/GHSA-c9vm-hv86-f23r

Vendor Advisories for CVE-2026-5388(1)

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

Affected Packages

(1 across 1 ecosystem)
PyPI(1)
PackageVulnerable rangeFix by version rangeDependents
justhtml0.1.0 ... 1.9.1 (59 versions)
  • every version up to 1.15.0: fixed in 1.15.0
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 35× in last 7d / 187× 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 322 total refreshes for this CVE.

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

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Frequently asked(5)

What is CVE-2026-5388?
CVE-2026-5388 is a critical vulnerability published on August 23, 2026. justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (cleanurlvalue/cleanurlinjsstring), HTML serialization, Markdown passthrough (htmlpassthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass…
When was CVE-2026-5388 disclosed?
CVE-2026-5388 was first published on August 23, 2026, with the most recent update on August 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-5388 actively exploited?
CVE-2026-5388 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.6% probability of exploitation in the next 30 days (46th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-5388?
CVE-2026-5388 has a CVSS base score of 9.8 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-5388?
A fix for CVE-2026-5388 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-5388 are linked in the Vendor Advisories panel on this page.

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