diff --git a/backend/package-lock.json b/backend/package-lock.json
index 8b1f948b..55949047 100644
--- a/backend/package-lock.json
+++ b/backend/package-lock.json
@@ -5947,9 +5947,9 @@
       }
     },
     "node_modules/nanoid": {
-      "version": "3.3.12",
-      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.12.tgz",
-      "integrity": "sha512-ZB9RH/39qpq5Vu6Y+NmUaFhQR6pp+M2Xt76XBnEwDaGcVAqhlvxrl3B2bKS5D3NH3QR76v3aSrKaF/Kiy7lEtQ==",
+      "version": "3.3.16",
+      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.16.tgz",
+      "integrity": "sha512-bzlKTyNJ7+LdGIIwy8ijFpIqEQIvafahV7eYykJ8Cvh42EdJeODoJ6gUJXpQJvej1BddH8OqTXZNE/KfbWAu8Q==",
       "funding": [
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@@ -6426,9 +6426,9 @@
       }
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     "node_modules/postcss": {
-      "version": "8.5.15",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.15.tgz",
-      "integrity": "sha512-FfR8sjd4em2T6fb3I2MwAJU7HWVMr9zba+enmQeeWFfCbm+UOC/0X4DS8XtpUTMwWMGbjKYP7xjfNekzyGmB3A==",
+      "version": "8.5.25",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.25.tgz",
+      "integrity": "sha512-DTPx3RWSSnWyzLxQnlH0rJP+EW5ekl16ZU4/psbIhA0e53kJfdgaN5vKM+xP7yJtXVu+nfdVFmlgFDEKAe4Pyw==",
       "funding": [
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@@ -6445,7 +6445,7 @@
       ],
       "license": "MIT",
       "dependencies": {
-        "nanoid": "^3.3.12",
+        "nanoid": "^3.3.16",
         "picocolors": "^1.1.1",
         "source-map-js": "^1.2.1"
       },
diff --git a/docs/release-log.md b/docs/release-log.md
index 0e2c2410..4d0c3e40 100644
--- a/docs/release-log.md
+++ b/docs/release-log.md
@@ -28,6 +28,7 @@ internal log into this file when they describe user-visible behavior.
 
 ## v2.3.0 — security + product-updates newsletter (2026-06-16)
 
+- Security (round 4): postcss 8.5.25 and tar 7.5.22 across all lockfiles, clearing 3 more advisories (2 high). react-router's 2 remaining high alerts need a 7→8 major and are held for founder sign-off.
 - Sheets: authors pick a typeface (Sans / Serif / Mono) and can add Note / Tip / Important / Warning / Definition callout blocks; readers get an "Aa" control for text size, reading width, and line height that persists across sheets.
 - Feed: posts now carry up to 5 attachments (PDF, images, JSON/TXT/CSV/MD) shown as a slideshow with prev/next paging, and "Download original" opens a picker that bundles the chosen files into a zip.
 - Security (round 3): cleared 9 fresh advisories — tar 7.5.21 (incl. a critical), fast-uri 4.1.1/off-4.x, js-yaml 4.3.0, body-parser 2.3.0 — lockfile-only; supersedes #439/#440.
diff --git a/frontend/studyhub-app/package-lock.json b/frontend/studyhub-app/package-lock.json
index ba9c3756..4d9da933 100644
--- a/frontend/studyhub-app/package-lock.json
+++ b/frontend/studyhub-app/package-lock.json
@@ -6493,9 +6493,9 @@
       }
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     "node_modules/postcss": {
-      "version": "8.5.19",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.19.tgz",
-      "integrity": "sha512-Mz8SaolMd8nB+G13WkORcxQKHZ/NE4xXevtkJHVuG+guo9/wYKlIMTKAqGdEmYOXR2ijPjTYNHssizdaVSUNdQ==",
+      "version": "8.5.25",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.25.tgz",
+      "integrity": "sha512-DTPx3RWSSnWyzLxQnlH0rJP+EW5ekl16ZU4/psbIhA0e53kJfdgaN5vKM+xP7yJtXVu+nfdVFmlgFDEKAe4Pyw==",
       "funding": [
         {
           "type": "opencollective",
@@ -6512,7 +6512,7 @@
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       "license": "MIT",
       "dependencies": {
-        "nanoid": "^3.3.12",
+        "nanoid": "^3.3.16",
         "picocolors": "^1.1.1",
         "source-map-js": "^1.2.1"
       },
@@ -7667,9 +7667,9 @@
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     "node_modules/tar": {
-      "version": "7.5.20",
-      "resolved": "https://registry.npmjs.org/tar/-/tar-7.5.20.tgz",
-      "integrity": "sha512-9FcyK4PA6+WbzlTM9WhQm6vB5W7cP7dUiPsv1g7YDwEQnQ1CGpK3MGlKk/ITVWMk05kHZuBhmVhiv8LZoy/PFQ==",
+      "version": "7.5.22",
+      "resolved": "https://registry.npmjs.org/tar/-/tar-7.5.22.tgz",
+      "integrity": "sha512-MFO/QzvtAOmJbkhOaCTvbGcFN9L9b+JunIsDwaKljSOdcLMea3NJ1k9Usz/rjdfSXTq4dfzfeS7W4p4YOAAHeA==",
       "license": "BlueOak-1.0.0",
       "dependencies": {
         "@isaacs/fs-minipass": "^4.0.0",
diff --git a/package-lock.json b/package-lock.json
index 02c89419..a71097fd 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -10649,9 +10649,9 @@
       }
     },
     "node_modules/nanoid": {
-      "version": "3.3.15",
-      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.15.tgz",
-      "integrity": "sha512-y7Wygv/7mEOvxTuEQDB8StXdMRBWf1kR/tlhAzBRUFkB2jfcLOAxO/SHmOO2zgz1pVgK29/kyupn059/bCHdjA==",
+      "version": "3.3.16",
+      "resolved": "https://registry.npmjs.org/nanoid/-/nanoid-3.3.16.tgz",
+      "integrity": "sha512-bzlKTyNJ7+LdGIIwy8ijFpIqEQIvafahV7eYykJ8Cvh42EdJeODoJ6gUJXpQJvej1BddH8OqTXZNE/KfbWAu8Q==",
       "funding": [
         {
           "type": "github",
@@ -11439,9 +11439,9 @@
       }
     },
     "node_modules/postcss": {
-      "version": "8.5.15",
-      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.15.tgz",
-      "integrity": "sha512-FfR8sjd4em2T6fb3I2MwAJU7HWVMr9zba+enmQeeWFfCbm+UOC/0X4DS8XtpUTMwWMGbjKYP7xjfNekzyGmB3A==",
+      "version": "8.5.25",
+      "resolved": "https://registry.npmjs.org/postcss/-/postcss-8.5.25.tgz",
+      "integrity": "sha512-DTPx3RWSSnWyzLxQnlH0rJP+EW5ekl16ZU4/psbIhA0e53kJfdgaN5vKM+xP7yJtXVu+nfdVFmlgFDEKAe4Pyw==",
       "funding": [
         {
           "type": "opencollective",
@@ -11458,7 +11458,7 @@
       ],
       "license": "MIT",
       "dependencies": {
-        "nanoid": "^3.3.12",
+        "nanoid": "^3.3.16",
         "picocolors": "^1.1.1",
         "source-map-js": "^1.2.1"
       },
@@ -13513,9 +13513,9 @@
       }
     },
     "node_modules/tar": {
-      "version": "7.5.21",
-      "resolved": "https://registry.npmjs.org/tar/-/tar-7.5.21.tgz",
-      "integrity": "sha512-XdhtCvlMywwxpCW8YEq3lOXBJpUPTR2OHHcwLPO3HwsJqOHa2Ok/oJ7ruGzp+JrKoRPVCzJwAdEjqLW/vNRPHA==",
+      "version": "7.5.22",
+      "resolved": "https://registry.npmjs.org/tar/-/tar-7.5.22.tgz",
+      "integrity": "sha512-MFO/QzvtAOmJbkhOaCTvbGcFN9L9b+JunIsDwaKljSOdcLMea3NJ1k9Usz/rjdfSXTq4dfzfeS7W4p4YOAAHeA==",
       "license": "BlueOak-1.0.0",
       "dependencies": {
         "@isaacs/fs-minipass": "^4.0.0",