Dancer2 versions before 2.2.0 for Perl serve a layout as a page when an equivalent spelling of its path misses the guard in the AutoPage handler.
The handler compares the request path against the layout directory name as text, while the lookup that follows canonicalises it. A doubled slash, a dot segment, a percent-encoded slash, or a different capitalisation on a case-insensitive filesystem therefore misses the guard.
The handler is off by default, enabled with auto_page. The layout wrapping every page is already public, so this discloses one of the application's other layouts.
CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).
No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (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