CVE-2026-55839
Stored XSS in Kestra UI via custom [[link]] markdown allowing JS injection.
Is CVE-2026-55839 being exploited?
Not confirmed. CVE-2026-55839 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 0.30% probability of exploitation in the next 30 days.
How severe is CVE-2026-55839?
CVE-2026-55839 is rated High with a CVSS score of 8.7. 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-2026-55839?
Yes. A fix has been recorded for CVE-2026-55839. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-55839 affect?
CVE-2026-55839 affects Kestra < 1.3.24, Kestra UI (ui/src/utils/markdown_plugins/link.ts). Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-55839?
Upgrade Kestra to v1.3.24 and sanitize/review existing Flow descriptions.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Stored XSS: attackers can execute arbitrary JavaScript in users' browsers, steal tokens/cookies, hijack sessions, or perform actions as victims when viewing Flow descriptions.
Patch when possible
- affected< 1.3.24
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.