CVE-2026-5388
justhtml <1.15.0 contains sanitization bypasses allowing active HTML/JS injection (XSS).
Is CVE-2026-5388 being exploited?
Not confirmed. CVE-2026-5388 does not appear in CISA's Known Exploited Vulnerabilities catalog, which records only exploitation that has been observed and reported publicly. That is evidence of absence of a report, not evidence the flaw is unattacked. EPSS currently estimates a 0.34% probability of exploitation in the next 30 days.
How severe is CVE-2026-5388?
CVE-2026-5388 is rated Critical with a CVSS score of 9.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2026-5388?
Yes. A fix has been recorded for CVE-2026-5388. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-5388 affect?
CVE-2026-5388 affects justhtml <1.15.0, Web applications using justhtml helper APIs, html_passthrough=True, or custom sanitization policies. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-5388?
Upgrade to justhtml >=1.15.0 and audit custom sanitize/transform policies
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Sanitization bypass enables stored/reflective XSS and arbitrary script execution via crafted URLs, markup, Markdown passthrough, or custom policies.
Immediate action required
- affected< 1.15.0
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.