CVE-2026-5388

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreHIGH 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 — 4 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%CVSS: 9.8Exploit: None knownExposed: 0

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

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
9.8(high)
EG Risk
59(Track)
EG Risk 59/100SSVC: Track

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%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
27%
KEV
Not listed

Published

August 23, 2026

Last Modified

August 26, 2026

Advisory Details (2)

Auto-updated Aug 26, 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
github Patch Available

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 rangeFixed inDependents
justhtml0.1.0 ... 1.9.1 (59 versions)1.15.0—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 30× in last 7d / 30× 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. 2026-08-26 21:39 UTCGHSA enrichment
  2. 2026-08-26 17:25 UTCEG score recompute
  3. 2026-08-26 17:25 UTCGHSA enrichment
  4. 2026-08-26 16:23 UTCEG score recompute
  5. 2026-08-26 16:23 UTCGHSA enrichment
  6. 2026-08-26 14:46 UTCEPSS rescore
  7. 2026-08-26 14:34 UTCGHSA enrichment
  8. 2026-08-26 10:21 UTCGHSA enrichment
  9. 2026-08-26 06:07 UTCGHSA enrichment
  10. 2026-08-26 01:53 UTCGHSA enrichment
  11. 2026-08-25 21:41 UTCGHSA enrichment
  12. 2026-08-25 17:03 UTCEG score recompute
  13. 2026-08-25 17:03 UTCGHSA enrichment
  14. 2026-08-25 13:49 UTCEPSS rescore
  15. 2026-08-25 12:47 UTCGHSA enrichment
  16. 2026-08-25 08:34 UTCGHSA enrichment
  17. 2026-08-25 04:21 UTCGHSA enrichment
  18. 2026-08-25 00:08 UTCGHSA enrichment
  19. 2026-08-24 19:55 UTCGHSA enrichment
  20. 2026-08-24 15:42 UTCEG score recompute
  21. 2026-08-24 15:42 UTCGHSA enrichment
  22. 2026-08-24 11:30 UTCGHSA enrichment
  23. 2026-08-24 07:17 UTCGHSA enrichment
  24. 2026-08-24 03:02 UTCGHSA enrichment
  25. 2026-08-23 22:47 UTCGHSA enrichment
Show 5 more
  1. 2026-08-23 18:33 UTCEG score recompute
  2. 2026-08-23 18:33 UTCGHSA enrichment
  3. 2026-08-23 14:20 UTCEG score recompute
  4. 2026-08-23 13:51 UTCEG score recompute
  5. 2026-08-23 13:50 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

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 in the National Vulnerability Database 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% probability of exploitation in the next 30 days, which ranks it in the top 72.9% of all scored CVEs.
What is the CVSS score of CVE-2026-5388?
CVE-2026-5388 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-5388?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-5388, 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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