diff --git a/.changeset/require-tarball-integrity.md b/.changeset/require-tarball-integrity.md
new file mode 100644
index 0000000000..f8c34b6467
--- /dev/null
+++ b/.changeset/require-tarball-integrity.md
@@ -0,0 +1,6 @@
+---
+"@pnpm/lockfile.utils": patch
+"pnpm": patch
+---
+
+Reject `pnpm-lock.yaml` entries whose remote tarball `resolution:` block is missing the `integrity` field. Previously the worker that extracts a downloaded tarball skipped hash verification when no integrity was supplied and minted a fresh one from the unverified bytes, so an attacker who could both alter the lockfile (e.g. via a pull request that strips `integrity:`) and serve modified content at the referenced tarball URL could install a tampered package without any error — including under `--frozen-lockfile`. pnpm now fails closed at lockfile-read time with `ERR_PNPM_MISSING_TARBALL_INTEGRITY`. Git-hosted tarballs (`gitHosted: true` or a URL on codeload.github.com / bitbucket.org / gitlab.com) and `file:` tarballs are exempt — the commit SHA in a git-host URL and the user-controlled local path already anchor the bytes.
diff --git a/lockfile/utils/package.json b/lockfile/utils/package.json
index e07ba2dff9..3d7041af46 100644
--- a/lockfile/utils/package.json
+++ b/lockfile/utils/package.json
@@ -34,6 +34,7 @@
   },
   "dependencies": {
     "@pnpm/dependency-path": "workspace:*",
+    "@pnpm/error": "workspace:*",
     "@pnpm/lockfile.types": "workspace:*",
     "@pnpm/resolver-base": "workspace:*",
     "@pnpm/types": "workspace:*",
diff --git a/lockfile/utils/src/pkgSnapshotToResolution.ts b/lockfile/utils/src/pkgSnapshotToResolution.ts
index 3f0e27b596..a24e4a7b8a 100644
--- a/lockfile/utils/src/pkgSnapshotToResolution.ts
+++ b/lockfile/utils/src/pkgSnapshotToResolution.ts
@@ -1,4 +1,5 @@
 import url from 'url'
+import { PnpmError } from '@pnpm/error'
 import { type PackageSnapshot, type TarballResolution } from '@pnpm/lockfile.types'
 import { type Resolution } from '@pnpm/resolver-base'
 import { type Registries } from '@pnpm/types'
@@ -10,10 +11,33 @@ export function pkgSnapshotToResolution (
   pkgSnapshot: PackageSnapshot,
   registries: Registries
 ): Resolution {
+  const resolution = pkgSnapshot.resolution as TarballResolution
+  // Tarball-shaped resolutions (no `type` field) must carry `integrity`,
+  // except where the URL itself anchors the bytes:
+  //   - `file:` tarballs (local file on the user's machine; integrity
+  //     adds nothing the user doesn't already control).
+  //   - Git-hosted tarballs (URL contains the commit SHA; git's content-
+  //     addressed model binds the bytes to the commit). The `gitHosted`
+  //     flag may be absent on legacy lockfiles, so fall back to a URL
+  //     match against the known git-host download endpoints.
+  // For any other tarball entry a missing integrity is what a tampered
+  // lockfile looks like: the worker would mint a fresh integrity from
+  // whatever bytes the URL returned, so we fail closed here.
   if (
-    Boolean((pkgSnapshot.resolution as TarballResolution).type) ||
-    (pkgSnapshot.resolution as TarballResolution).tarball?.startsWith('file:') ||
-    (pkgSnapshot.resolution as TarballResolution).gitHosted === true
+    resolution.type == null &&
+    resolution.integrity == null &&
+    !resolution.tarball?.startsWith('file:') &&
+    !(resolution.gitHosted === true || (resolution.tarball != null && isGitHostedTarballUrl(resolution.tarball)))
+  ) {
+    throw new PnpmError('MISSING_TARBALL_INTEGRITY',
+      `Cannot install package "${depPath}": its lockfile entry has no "integrity" field, so pnpm cannot verify the downloaded tarball.`,
+      { hint: 'The lockfile may be corrupted or have been tampered with. Restore it from a trusted source, or delete it and re-run installation without --frozen-lockfile to regenerate.' }
+    )
+  }
+  if (
+    Boolean(resolution.type) ||
+    resolution.tarball?.startsWith('file:') ||
+    resolution.gitHosted === true
   ) {
     return pkgSnapshot.resolution as Resolution
   }
@@ -47,3 +71,15 @@ export function pkgSnapshotToResolution (
     return getNpmTarballUrl(name, version, { registry })
   }
 }
+
+// Fallback for legacy lockfile entries whose tarball resolution lacks the
+// `gitHosted` flag. Matches the known git-host download endpoints so a URL
+// rewritten by pnpm's git resolver is still recognized as content-addressed
+// and exempt from the integrity requirement.
+function isGitHostedTarballUrl (url: string): boolean {
+  return (
+    url.startsWith('https://codeload.github.com/') ||
+    url.startsWith('https://bitbucket.org/') ||
+    url.startsWith('https://gitlab.com/')
+  )
+}
diff --git a/lockfile/utils/test/pkgSnapshotToResolution.ts b/lockfile/utils/test/pkgSnapshotToResolution.ts
index bfb34f65df..cce4b79da0 100644
--- a/lockfile/utils/test/pkgSnapshotToResolution.ts
+++ b/lockfile/utils/test/pkgSnapshotToResolution.ts
@@ -32,9 +32,67 @@ test('pkgSnapshotToResolution()', () => {
 
   expect(pkgSnapshotToResolution('@cdn.sheetjs.com/xlsx-0.18.9/xlsx-0.18.9.tgz', {
     resolution: {
+      integrity: 'sha512-CCCC',
       tarball: 'https://cdn.sheetjs.com/xlsx-0.18.9/xlsx-0.18.9.tgz',
     },
   }, { default: 'https://registry.npmjs.org/' })).toEqual({
+    integrity: 'sha512-CCCC',
     tarball: 'https://cdn.sheetjs.com/xlsx-0.18.9/xlsx-0.18.9.tgz',
   })
 })
+
+test('pkgSnapshotToResolution() rejects a remote tarball resolution that has no integrity', () => {
+  // A tampered or malformed lockfile that strips the `integrity` field
+  // would otherwise let pnpm download the URL contents unchecked. The
+  // helper must fail closed so neither install path nor any read-only
+  // consumer (sbom, list, etc.) silently trusts the lockfile entry.
+  expect(() => pkgSnapshotToResolution('foo@1.0.0', {
+    resolution: {
+      tarball: 'https://registry.npmjs.org/foo/-/foo-1.0.0.tgz',
+    },
+  }, { default: 'https://registry.npmjs.org/' })).toThrow(expect.objectContaining({ code: 'ERR_PNPM_MISSING_TARBALL_INTEGRITY' }))
+
+  // A tarball URL on an arbitrary CDN (no `gitHosted` flag, no known git
+  // host pattern) is still a regular remote tarball — integrity required.
+  expect(() => pkgSnapshotToResolution('xlsx@https+++cdn.sheetjs.com+xlsx-0.18.9+xlsx-0.18.9.tgz', {
+    resolution: {
+      tarball: 'https://cdn.sheetjs.com/xlsx-0.18.9/xlsx-0.18.9.tgz',
+    },
+  }, { default: 'https://registry.npmjs.org/' })).toThrow(expect.objectContaining({ code: 'ERR_PNPM_MISSING_TARBALL_INTEGRITY' }))
+})
+
+test('pkgSnapshotToResolution() allows git-hosted and file: tarballs to lack integrity', () => {
+  // Git-hosted tarballs are anchored by the commit SHA in their URL —
+  // pnpm's own install pipeline writes them without `integrity:` (see
+  // the `with-git-protocol-dep` fixture). Both the explicit
+  // `gitHosted: true` flag and a URL on a known git host must bypass
+  // the integrity check.
+  expect(pkgSnapshotToResolution('foo@https+++github.com+foo+bar', {
+    resolution: {
+      tarball: 'https://codeload.github.com/foo/bar/tar.gz/abc1234',
+      gitHosted: true,
+    },
+  }, { default: 'https://registry.npmjs.org/' })).toEqual({
+    tarball: 'https://codeload.github.com/foo/bar/tar.gz/abc1234',
+    gitHosted: true,
+  })
+
+  expect(pkgSnapshotToResolution('is-negative@https+++codeload.github.com+kevva+is-negative+tar.gz+abc', {
+    resolution: {
+      tarball: 'https://codeload.github.com/kevva/is-negative/tar.gz/abc1234',
+    },
+  }, { default: 'https://registry.npmjs.org/' })).toEqual({
+    tarball: 'https://codeload.github.com/kevva/is-negative/tar.gz/abc1234',
+  })
+
+  // `file:` tarballs are local files; the user already controls the
+  // bytes, and the install pipeline may write them without integrity.
+  expect(pkgSnapshotToResolution('local-pkg@file:local-pkg-1.0.0.tgz', {
+    resolution: {
+      tarball: 'file:local-pkg-1.0.0.tgz',
+    },
+    version: '1.0.0',
+  }, { default: 'https://registry.npmjs.org/' })).toEqual({
+    tarball: 'file:local-pkg-1.0.0.tgz',
+  })
+})
diff --git a/lockfile/utils/tsconfig.json b/lockfile/utils/tsconfig.json
index e6aee5c316..dc3564a8aa 100644
--- a/lockfile/utils/tsconfig.json
+++ b/lockfile/utils/tsconfig.json
@@ -12,6 +12,9 @@
     {
       "path": "../../packages/dependency-path"
     },
+    {
+      "path": "../../packages/error"
+    },
     {
       "path": "../../packages/types"
     },
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 9023568e5e..6ed4b44ac2 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -4054,6 +4054,9 @@ importers:
       '@pnpm/dependency-path':
         specifier: workspace:*
         version: link:../../packages/dependency-path
+      '@pnpm/error':
+        specifier: workspace:*
+        version: link:../../packages/error
       '@pnpm/lockfile.types':
         specifier: workspace:*
         version: link:../types