fix: add system UID range validation to prevent privilege escalation #267

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Merged

Mossaka merged 4 commits into main from copilot/add-uid-gid-range-check

Jan 17, 2026

src/docker-manager.test.ts

-Original file line number
+Diff line change
@@ -1,4 +1,4 @@
-    import { generateDockerCompose, subnetsOverlap, writeConfigs, startContainers, stopContainers, cleanup, runAgentCommand } from './docker-manager';
+    import { generateDockerCompose, subnetsOverlap, writeConfigs, startContainers, stopContainers, cleanup, runAgentCommand, validateIdNotInSystemRange, getSafeHostUid, getSafeHostGid, MIN_REGULAR_UID } from './docker-manager';
     import { WrapperConfig } from './types';
     import * as fs from 'fs';
     import * as path from 'path';
@@ Expand All / @@ -10,8 +10,8 @@ @@
     // Mock execa module
     jest.mock('execa', () => {
       const fn = (...args: any[]) => mockExecaFn(...args);
       fn.sync = (...args: any[]) => mockExecaSync(...args);
       return fn;
     });
@@ Expand Down Expand Up / @@ -47,6 +47,127 @@ @@
         });
       });
+      describe('validateIdNotInSystemRange', () => {
+        it('should return 1000 for system UIDs (0-999)', () => {
+          expect(validateIdNotInSystemRange(0)).toBe('1000');
+          expect(validateIdNotInSystemRange(1)).toBe('1000');
+          expect(validateIdNotInSystemRange(13)).toBe('1000'); // proxy user
+          expect(validateIdNotInSystemRange(999)).toBe('1000');
+        });
+        it('should return the UID as-is for regular users (>= 1000)', () => {
+          expect(validateIdNotInSystemRange(1000)).toBe('1000');
+          expect(validateIdNotInSystemRange(1001)).toBe('1001');
+          expect(validateIdNotInSystemRange(65534)).toBe('65534'); // nobody user on some systems
+        });
+      });
+      describe('getSafeHostUid', () => {
+        const originalGetuid = process.getuid;
+        const originalSudoUid = process.env.SUDO_UID;
+        afterEach(() => {
+          process.getuid = originalGetuid;
+          if (originalSudoUid !== undefined) {
+            process.env.SUDO_UID = originalSudoUid;
+          } else {
+            delete process.env.SUDO_UID;
+          }
+        });
+        it('should return 1000 when SUDO_UID is a system UID', () => {
+          process.getuid = () => 0; // Running as root
+          process.env.SUDO_UID = '13'; // proxy user
+          expect(getSafeHostUid()).toBe('1000');
+        });
+        it('should return SUDO_UID when it is a regular user UID', () => {
+          process.getuid = () => 0; // Running as root
+          process.env.SUDO_UID = '1001';
+          expect(getSafeHostUid()).toBe('1001');
+        });
+        it('should return 1000 when SUDO_UID is 0', () => {
+          process.getuid = () => 0; // Running as root
+          process.env.SUDO_UID = '0';
+          expect(getSafeHostUid()).toBe('1000');
+        });
+        it('should return 1000 when running as root without SUDO_UID', () => {
+          process.getuid = () => 0;
+          delete process.env.SUDO_UID;
+          expect(getSafeHostUid()).toBe('1000');
+        });
+        it('should return 1000 for non-root system UID', () => {
+          process.getuid = () => 13; // proxy user
+          delete process.env.SUDO_UID;
+          expect(getSafeHostUid()).toBe('1000');
+        });
+        it('should return the UID when running as regular user', () => {
+          process.getuid = () => 1001;
+          delete process.env.SUDO_UID;
+          expect(getSafeHostUid()).toBe('1001');
+        });
+      });
+      describe('getSafeHostGid', () => {
+        const originalGetgid = process.getgid;
+        const originalSudoGid = process.env.SUDO_GID;
+        afterEach(() => {
+          process.getgid = originalGetgid;
+          if (originalSudoGid !== undefined) {
+            process.env.SUDO_GID = originalSudoGid;
+          } else {
+            delete process.env.SUDO_GID;
+          }
+        });
+        it('should return 1000 when SUDO_GID is a system GID', () => {
+          process.getgid = () => 0; // Running as root
+          process.env.SUDO_GID = '13'; // proxy group
+          expect(getSafeHostGid()).toBe('1000');
+        });
+        it('should return SUDO_GID when it is a regular user GID', () => {
+          process.getgid = () => 0; // Running as root
+          process.env.SUDO_GID = '1001';
+          expect(getSafeHostGid()).toBe('1001');
+        });
+        it('should return 1000 when SUDO_GID is 0', () => {
+          process.getgid = () => 0; // Running as root
+          process.env.SUDO_GID = '0';
+          expect(getSafeHostGid()).toBe('1000');
+        });
+        it('should return 1000 when running as root without SUDO_GID', () => {
+          process.getgid = () => 0;
+          delete process.env.SUDO_GID;
+          expect(getSafeHostGid()).toBe('1000');
+        });
+        it('should return 1000 for non-root system GID', () => {
+          process.getgid = () => 13; // proxy group
+          delete process.env.SUDO_GID;
+          expect(getSafeHostGid()).toBe('1000');
+        });
+        it('should return the GID when running as regular user', () => {
+          process.getgid = () => 1001;
+          delete process.env.SUDO_GID;
+          expect(getSafeHostGid()).toBe('1001');
+        });
+      });
+      describe('MIN_REGULAR_UID constant', () => {
+        it('should be 1000 (standard Linux regular user UID threshold)', () => {
+          expect(MIN_REGULAR_UID).toBe(1000);
+        });
+      });
       describe('generateDockerCompose', () => {
         const mockConfig: WrapperConfig = {
           allowedDomains: ['github.com', 'npmjs.org'],
@@ Expand Down Expand Up / @@ -660,8 +781,8 @@ @@
         });
         it('should remove existing containers before starting', async () => {
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           await startContainers(testDir, ['github.com']);
@@ Expand All / @@ -673,8 +794,8 @@ @@
         });
         it('should run docker compose up', async () => {
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           await startContainers(testDir, ['github.com']);
@@ Expand All / @@ -686,7 +807,7 @@ @@
         });
         it('should handle docker compose failure', async () => {
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           mockExecaFn.mockRejectedValueOnce(new Error('Docker compose failed'));
           await expect(startContainers(testDir, ['github.com'])).rejects.toThrow('Docker compose failed');
@@ Expand All / @@ -701,7 +822,7 @@ @@
             '1760994429.358 172.30.0.20:36274 blocked.com:443 -:- 1.1 CONNECT 403 TCP_DENIED:HIER_NONE blocked.com:443 "curl/7.81.0"\n'
           );
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           mockExecaFn.mockRejectedValueOnce(new Error('is unhealthy'));
           await expect(startContainers(testDir, ['github.com'])).rejects.toThrow();
@@ Expand Down Expand Up / @@ -729,7 +850,7 @@ @@
         });
         it('should run docker compose down when keepContainers is false', async () => {
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           await stopContainers(testDir, false);
@@ Expand Down Expand Up / @@ -763,7 +884,7 @@ @@
         it('should return exit code from container', async () => {
           // Mock docker logs -f
           mockExecaFn.mockResolvedValueOnce({ stdout: '', stderr: '', exitCode: 0 } as any);
           // Mock docker wait
           mockExecaFn.mockResolvedValueOnce({ stdout: '0', stderr: '', exitCode: 0 } as any);
@@ Expand Down @@

src/docker-manager.ts

            
                      Original file line number
                      Diff line number
                      Diff line change
                  
    @@ -12,41 +12,70 @@ const SQUID_PORT = 3128;
  
    const SQUID_INTERCEPT_PORT = 3129; // Port for transparently intercepted traffic

    /**

     * Gets the host user's UID, with fallback to 1000 if unavailable or root (0).

     * Minimum UID/GID value for regular users.

     * UIDs 0-999 are reserved for system users on most Linux distributions.

     */

    export const MIN_REGULAR_UID = 1000;

    /**

     * Validates that a UID/GID value is safe for use (not in system range).

     * Returns the value if valid, or the default (1000) if in system range.

     * @internal Exported for testing

     */

    export function validateIdNotInSystemRange(id: number): string {

      // Reject system UIDs/GIDs (0-999) - use default unprivileged user instead

      if (id < MIN_REGULAR_UID) {

        return MIN_REGULAR_UID.toString();

      }

      return id.toString();

    }

    /**

     * Gets the host user's UID, with fallback to 1000 if unavailable, root (0),

     * or in the system UID range (0-999).

     * When running with sudo, uses SUDO_UID to get the actual user's UID.

     * @internal Exported for testing

     */

    function getSafeHostUid(): string {

    export function getSafeHostUid(): string {

      const uid = process.getuid?.();

      // When running as root (sudo), try to get the original user's UID

      if (!uid || uid === 0) {

        const sudoUid = process.env.SUDO_UID;

        if (sudoUid && sudoUid !== '0') {

          return sudoUid;

        if (sudoUid) {

          const parsedUid = parseInt(sudoUid, 10);

          if (!isNaN(parsedUid)) {

            return validateIdNotInSystemRange(parsedUid);

          }

        }

        return '1000';

        return MIN_REGULAR_UID.toString();

      }

      return uid.toString();

      return validateIdNotInSystemRange(uid);

    }

    /**

     * Gets the host user's GID, with fallback to 1000 if unavailable or root (0).

     * Gets the host user's GID, with fallback to 1000 if unavailable, root (0),

     * or in the system GID range (0-999).

     * When running with sudo, uses SUDO_GID to get the actual user's GID.

     * @internal Exported for testing

     */

    function getSafeHostGid(): string {

    export function getSafeHostGid(): string {

      const gid = process.getgid?.();

      // When running as root (sudo), try to get the original user's GID

      if (!gid || gid === 0) {

        const sudoGid = process.env.SUDO_GID;

        if (sudoGid && sudoGid !== '0') {

          return sudoGid;

        if (sudoGid) {

          const parsedGid = parseInt(sudoGid, 10);

          if (!isNaN(parsedGid)) {

            return validateIdNotInSystemRange(parsedGid);

          }

        }

        return '1000';

        return MIN_REGULAR_UID.toString();

      }

      return gid.toString();

      return validateIdNotInSystemRange(gid);

    }

    /**

fix: add system UID range validation to prevent privilege escalation #267

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