DOMPurify's ADD_TAGS function form bypasses FORBID_TAGS due to short-circuit evaluation

## 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)

Source published

16 Apr 2026 00:46:35 UTC

Source modified

10 Sep 2026 03:50:42 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V4 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N

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