diff --git a/app/client/ui/AdminPanel.ts b/app/client/ui/AdminPanel.ts
index bfd2bd6c..91f6802b 100644
--- a/app/client/ui/AdminPanel.ts
+++ b/app/client/ui/AdminPanel.ts
@@ -145,6 +145,13 @@ Please log in as an administrator.`)),
           description: t('Current authentication method'),
           value: this._buildAuthenticationDisplay(owner),
           expandedContent: this._buildAuthenticationNotice(owner),
+        }),
+        dom.create(AdminSectionItem, {
+          id: 'session',
+          name: t('Session Secret'),
+          description: t('Key to sign sessions with'),
+          value: this._buildSessionSecretDisplay(owner),
+          expandedContent: this._buildSessionSecretNotice(owner),
         })
       ]),
       dom.create(AdminSection, t('Version'), [
@@ -241,6 +248,27 @@ We recommend enabling one of these if Grist is accessible over the network or be
 to multiple people.');
   }
 
+  private _buildSessionSecretDisplay(owner: IDisposableOwner) {
+    return dom.domComputed(
+      use => {
+        const req = this._checks.requestCheckById(use, 'session-secret');
+        const result = req ? use(req.result) : undefined;
+
+        if (result?.status === 'warning') {
+          return cssValueLabel(cssDangerText('default'));
+        }
+
+        return cssValueLabel(cssHappyText('configured'));
+      }
+    );
+  }
+
+  private _buildSessionSecretNotice(owner: IDisposableOwner) {
+    return t('Grist signs user session cookies with a secret key. Please set this key via the environment variable \
+GRIST_SESSION_SECRET. Grist falls back to a hard-coded default when it is not set. We may remove this notice \
+in the future as session IDs generated since v1.1.16 are inherently cryptographically secure.');
+  }
+
   private _buildUpdates(owner: MultiHolder) {
     // We can be in those states:
     enum State {
@@ -472,7 +500,11 @@ to multiple people.');
     return dom.domComputed(
       use => [
         ...use(this._checks.probes).map(probe => {
-          const isRedundant = probe.id === 'sandboxing';
+          const isRedundant = [
+            'sandboxing',
+            'authentication',
+            'session-secret'
+          ].includes(probe.id);
           const show = isRedundant ? options.showRedundant : options.showNovel;
           if (!show) { return null; }
           const req = this._checks.requestCheck(probe);
diff --git a/app/common/BootProbe.ts b/app/common/BootProbe.ts
index 49fb9911..c73843b1 100644
--- a/app/common/BootProbe.ts
+++ b/app/common/BootProbe.ts
@@ -8,7 +8,8 @@ export type BootProbeIds =
     'sandboxing' |
     'system-user' |
     'authentication' |
-    'websockets'
+    'websockets' |
+    'session-secret'
 ;
 
 export interface BootProbeResult {
diff --git a/app/server/lib/BootProbes.ts b/app/server/lib/BootProbes.ts
index 61ac66eb..adef4811 100644
--- a/app/server/lib/BootProbes.ts
+++ b/app/server/lib/BootProbes.ts
@@ -6,6 +6,7 @@ import { GristServer } from 'app/server/lib/GristServer';
 import * as express from 'express';
 import WS from 'ws';
 import fetch from 'node-fetch';
+import { DEFAULT_SESSION_SECRET } from 'app/server/lib/coreCreator';
 
 /**
  * Self-diagnostics useful when installing Grist.
@@ -61,6 +62,7 @@ export class BootProbes {
     this._probes.push(_sandboxingProbe);
     this._probes.push(_authenticationProbe);
     this._probes.push(_webSocketsProbe);
+    this._probes.push(_sessionSecretProbe);
     this._probeById = new Map(this._probes.map(p => [p.id, p]));
   }
 }
@@ -284,3 +286,17 @@ const _authenticationProbe: Probe = {
     };
   },
 };
+
+const _sessionSecretProbe: Probe = {
+  id: 'session-secret',
+  name: 'Session secret',
+  apply: async(server, req) => {
+    const usingDefaultSessionSecret = server.create.sessionSecret() === DEFAULT_SESSION_SECRET;
+    return {
+      status: usingDefaultSessionSecret ? 'warning' : 'success',
+      details: {
+        "GRIST_SESSION_SECRET": process.env.GRIST_SESSION_SECRET ? "set" : "not set",
+      }
+    };
+  },
+};
diff --git a/app/server/lib/coreCreator.ts b/app/server/lib/coreCreator.ts
index f4536c16..477c970b 100644
--- a/app/server/lib/coreCreator.ts
+++ b/app/server/lib/coreCreator.ts
@@ -3,11 +3,14 @@ import { checkMinIOBucket, checkMinIOExternalStorage,
 import { makeSimpleCreator } from 'app/server/lib/ICreate';
 import { Telemetry } from 'app/server/lib/Telemetry';
 
+export const DEFAULT_SESSION_SECRET =
+  'Phoo2ag1jaiz6Moo2Iese2xoaphahbai3oNg7diemohlah0ohtae9iengafieS2Hae7quungoCi9iaPh';
+
 export const makeCoreCreator = () => makeSimpleCreator({
   deploymentType: 'core',
   // This can and should be overridden by GRIST_SESSION_SECRET
   // (or generated randomly per install, like grist-omnibus does).
-  sessionSecret: 'Phoo2ag1jaiz6Moo2Iese2xoaphahbai3oNg7diemohlah0ohtae9iengafieS2Hae7quungoCi9iaPh',
+  sessionSecret: DEFAULT_SESSION_SECRET,
   storage: [
     {
       name: 'minio',
diff --git a/app/server/lib/gristSessions.ts b/app/server/lib/gristSessions.ts
index 987fae58..a5555ba1 100644
--- a/app/server/lib/gristSessions.ts
+++ b/app/server/lib/gristSessions.ts
@@ -6,10 +6,10 @@ import {GristServer} from 'app/server/lib/GristServer';
 import {fromCallback} from 'app/server/lib/serverUtils';
 import {Sessions} from 'app/server/lib/Sessions';
 import {promisifyAll} from 'bluebird';
+import * as crypto from 'crypto';
 import * as express from 'express';
 import assignIn = require('lodash/assignIn');
 import * as path from 'path';
-import * as shortUUID from "short-uuid";
 
 
 export const cookieName = process.env.GRIST_SESSION_COOKIE || 'grist_sid';
@@ -118,7 +118,10 @@ export function initGristSessions(instanceRoot: string, server: GristServer) {
   // cookie could be stolen (with some effort) by the custom domain's owner, we limit the damage
   // by only honoring custom-domain cookies for requests to that domain.
   const generateId = (req: RequestWithOrg) => {
-    const uid = shortUUID.generate();
+    // Generate 256 bits of cryptographically random data to use as the session ID.
+    // This ensures security against brute-force session hijacking even without signing the session ID.
+    const randomNumbers = crypto.getRandomValues(new Uint8Array(32));
+    const uid = Buffer.from(randomNumbers).toString("hex");
     return req.isCustomHost ? `c-${uid}@${req.org}@${req.get('host')}` : `g-${uid}`;
   };
   const sessionSecret = server.create.sessionSecret();
diff --git a/static/locales/en.client.json b/static/locales/en.client.json
index 7a8ee8df..baae4538 100644
--- a/static/locales/en.client.json
+++ b/static/locales/en.client.json
@@ -1541,6 +1541,7 @@
         "Error": "Error",
         "Error checking for updates": "Error checking for updates",
         "Grist allows for very powerful formulas, using Python. We recommend setting the environment variable GRIST_SANDBOX_FLAVOR to gvisor if your hardware supports it (most will), to run formulas in each document within a sandbox isolated from other documents and isolated from the network.": "Grist allows for very powerful formulas, using Python. We recommend setting the environment variable GRIST_SANDBOX_FLAVOR to gvisor if your hardware supports it (most will), to run formulas in each document within a sandbox isolated from other documents and isolated from the network.",
+        "Grist signs user session cookies with a secret key. Please set this key via the environment variable GRIST_SESSION_SECRET. Grist falls back to a hard-coded default when it is not set. We may remove this notice in the future since session IDs have been updated to be inherently cryptographically secure.": "Grist signs user session cookies with a secret key. Please set this key via the environment variable GRIST_SESSION_SECRET. Grist falls back to a hard-coded default when it is not set. We may remove this notice in the future as session IDs generated since v1.1.16 are inherently cryptographically secure.",
         "Grist is up to date": "Grist is up to date",
         "Grist releases are at ": "Grist releases are at ",
         "Last checked {{time}}": "Last checked {{time}}",