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Improve session ID security (#1059)

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Follow-up of #994. This PR revises the session ID generation logic to improve security in the absence of a secure session secret. It also adds a section in the admin panel "security" section to nag system admins when GRIST_SESSION_SECRET is not set.

Following is an excerpt from internal conversation.

TL;DR: Grist's current implementation generates semi-secure session IDs and uses a publicly known default signing key to sign them when the environment variable GRIST_SESSION_SECRET is not set. This PR generates cryptographically secure session IDs to dismiss security concerns around an insecure signing key, and encourages system admins to configure their own signing key anyway.

> The session secret is required by expressjs/session to sign its session IDs. It's designed as an extra protection against session hijacking by randomly guessing session IDs and hitting a valid one. While it is easy to encourage users to set a distinct session secret, this is unnecessary if session IDs are generated in a cryptographically secure way. As of now Grist uses version 4 UUIDs as session IDs (see app/server/lib/gristSessions.ts - it uses shortUUID.generate which invokes uuid.v4 under the hood). These contain 122 bits of entropy, technically insufficient to be considered cryptographically secure. In practice, this is never considered a real vulnerability. To compare, RSA2048 is still very commonly used in web servers, yet it only has 112 bits of security (>=128 bits = "secure", rule of thumb in cryptography). But for peace of mind I propose using crypto.getRandomValues to generate real 128-bit random values. This should render session ID signing unnecessary and hence dismiss security concerns around an insecure signing key.
This commit is contained in:
Leslie H
2024-06-25 15:43:25 -04:00
committed by GitHub
parent 550c39156b
commit 24ce54b586
6 changed files with 61 additions and 5 deletions
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static/locales/en.client.json
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@@ -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}}",