CVE-2026-65903

## Summary In `src/purify.ts:1117-1123`, `ADD_TAGS` as a function (via `EXTRA_ELEMENT_HANDLING.tagCheck`) bypasses `FORBID_TAGS` due to short-circuit evaluation. The condition: ``` !(tagCheck(tagName)) && (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName]) ``` When `tagCheck(tagName)` returns `true`, the entire condition is `false` and the element is kept — `FORBID_TAGS[tagName]` is never evaluated. ## Inconsistency This contradicts the attribute-side pattern at line 1214 where `FORBID_ATTR` explicitly wins first: ``` if (FORBID_ATTR[lcName]) { continue; } ``` For tags, FORBID should also take precedence over ADD. ## Impact Applications using both `ADD_TAGS` as a function and `FORBID_TAGS` simultaneously get unexpected behavior — forbidden tags are allowed through. Config-dependent but a genuine logic inconsistency. ## Suggested Fix Check `FORBID_TAGS` before `tagCheck`: ``` if (FORBID_TAGS[tagName]) { /* remove */ } else if (tagCheck(tagName) || ALLOWED_TAGS[tagName]) { /* keep */ } ``` ## Affected Version v3.3.3 (commit 883ac15)

## Summary In `src/purify.ts:1117-1123`, `ADD_TAGS` as a function (via `EXTRA_ELEMENT_HANDLING.tagCheck`) bypasses `FORBID_TAGS` due to short-circuit evaluation. The condition: ``` !(tagCheck(tagName)) && (!ALLOWED_TAGS[tagName] || FORBID_TAGS[tagName]) ``` When `tagCheck(tagName)` returns `true`, the entire condition is `false` and the element is kept — `FORBID_TAGS[tagName]` is never evaluated. ## Inconsistency This contradicts the attribute-side pattern at line 1214 where `FORBID_ATTR` explicitly wins first: ``` if (FORBID_ATTR[lcName]) { continue; } ``` For tags, FORBID should also take precedence over ADD. ## Impact Applications using both `ADD_TAGS` as a function and `FORBID_TAGS` simultaneously get unexpected behavior — forbidden tags are allowed through. Config-dependent but a genuine logic inconsistency. ## Suggested Fix Check `FORBID_TAGS` before `tagCheck`: ``` if (FORBID_TAGS[tagName]) { /* remove */ } else if (tagCheck(tagName) || ALLOWED_TAGS[tagName]) { /* keep */ } ``` ## Affected Version v3.3.3 (commit 883ac15)

DOMPurify anterior a la versión 3.4.0 contiene un error lógico en la función ADD_TAGS donde la evaluación de cortocircuito permite que las etiquetas prohibidas eludan las restricciones de FORBID_TAGS. Los atacantes pueden elaborar una entrada que contenga etiquetas listadas en FORBID_TAGS que también se añaden a través de la función ADD_TAGS, provocando que se retengan en la salida saneada.