CVE-2026-55674
Unauthenticated cookie-based HTML injection in Discourse allows arbitrary JS execution.
Is CVE-2026-55674 being exploited?
Not confirmed. CVE-2026-55674 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 0.36% probability of exploitation in the next 30 days.
How severe is CVE-2026-55674?
CVE-2026-55674 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-2026-55674?
Yes. A fix has been recorded for CVE-2026-55674. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2026-55674 affect?
CVE-2026-55674 affects Discourse < 2026.1.6, Discourse < 2026.5.2, Discourse < 2026.6.1, Discourse < 2026.7.0. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
What should I do about CVE-2026-55674?
Upgrade Discourse to the listed fixed versions and validate cookie handling/CSP.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
Unauthenticated attacker can inject HTML/JS via crafted cookie, bypass CSP and run arbitrary JavaScript in visitors' browsers (session theft, account compromise, malware delivery).
Immediate action required
- affected< 2026.1.6
- affected>= 2026.5.0-latest and < 2026.5.2
- affected>= 2026.6.0-latest and < 2026.6.1
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.