diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 520eadf03b..cac5c54c86 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -33,6 +33,7 @@ overrides:
   '@hono/node-server@<3.0.0': ^2.0.10
   fast-uri@<4.0.0: ^3.1.5
   hono@<5.0.0: ^4.12.34
+  dompurify@<4.0.0: ^3.4.13
 
 importers:
 
@@ -5777,8 +5778,8 @@ packages:
   dom-accessibility-api@0.5.16:
     resolution: {integrity: sha512-X7BJ2yElsnOJ30pZF4uIIDfBEVgF4XEBxL9Bxhy6dnrm5hkzqmsWHGTiHqRiITNhMyFLyAiWndIJP7Z1NTteDg==}
 
-  dompurify@3.4.12:
-    resolution: {integrity: sha512-zQvGet8Z2sWbQhCmfFz/T5QWH2oBmjnqK3qvOjaqaNLrLEF912WamU+ohnTp0TCep/MFVHpdJuCZEdFOdTnEFg==}
+  dompurify@3.4.13:
+    resolution: {integrity: sha512-2vmYIoqjze2d+kakP8S/nS5shfsl587kzwEjcGlTdiksUVgFHnFCsLYDVj/JNqJVOQZGSYBTmuycv0PodwmnMQ==}
 
   dotenv-flow@4.1.0:
     resolution: {integrity: sha512-0cwP9jpQBQfyHwvE0cRhraZMkdV45TQedA8AAUZMsFzvmLcQyc1HPv+oX0OOYwLFjIlvgVepQ+WuQHbqDaHJZg==}
@@ -12090,7 +12091,7 @@ snapshots:
 
   dom-accessibility-api@0.5.16: {}
 
-  dompurify@3.4.12:
+  dompurify@3.4.13:
     optionalDependencies:
       '@types/trusted-types': 2.0.7
 
@@ -13650,7 +13651,7 @@ snapshots:
       d3-sankey: 0.12.3
       dagre-d3-es: 7.0.14
       dayjs: 1.11.21
-      dompurify: 3.4.12
+      dompurify: 3.4.13
       es-toolkit: 1.49.0
       katex: 0.16.47
       khroma: 2.1.0
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index f20dee1b17..b0edbec496 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -192,3 +192,21 @@ overrides:
   #     compatibility. check-override-consistency.mjs covers both forms.
   'fast-uri@<4.0.0': '^3.1.5'
   'hono@<5.0.0': '^4.12.34'
+  # OSV 2026-08-07 (#6407) — transitive-only, and the same "it has a fix, so
+  # take the fix" disposition as the batch above:
+  #   dompurify GHSA-55q2-fjhq-7xh7 (5.1 medium) — an IN_PLACE hook removal
+  #     leaves a detached subtree executable (XSS). Advisory range is
+  #     introduced:0 → fixed:3.4.13, i.e. every version up to and including
+  #     3.4.12 is affected, so the selector's floor is the package floor and
+  #     only the upper bound needs stating. Transitive-only via mermaid
+  #     (apps/docs declares mermaid ^11.16.0; mermaid@11.16.1 declares
+  #     dompurify ^3.3.3). Nothing in this workspace declares dompurify
+  #     directly, so there is no publishable manifest to keep in lockstep —
+  #     check-override-consistency.mjs will list this as an override it cannot
+  #     cross-check against a declared range, which is correct for this shape.
+  #     ^3.4.13 sits INSIDE mermaid's own ^3.3.3 range, so this is a dedupe onto
+  #     the patched line rather than a forced upgrade past what mermaid supports.
+  #     Bound at the 4.0.0 major boundary per this block's header rule — never
+  #     `<3.4.13`, which would self-invalidate the day 3.4.13 is itself flagged
+  #     (the undici 7.28.0 / brace-expansion 5.0.8 specimens, #4961 / #5032).
+  'dompurify@<4.0.0': '^3.4.13'