CVE-2025-53940: Quiet Auth Bypass Vulnerability

CVE-2025-53940 Overview

CVE-2025-53940 is a timing attack vulnerability in Quiet, a decentralized team chat application that serves as an alternative to Slack, Discord, and Element. The flaw exists in Quiet's backend and frontend communication API, which used a non constant-time comparison function for token verification. Versions 6.1.0-alpha.4 and below are affected. An attacker on the local system can submit token guesses and measure response timing differences to recover the token one character at a time. The issue is fixed in version 6.0.1 and is tracked under [CWE-208] (Observable Timing Discrepancy).

Critical Impact
Successful exploitation allows an attacker to recover the API authentication token, granting unauthorized access to backend functionality and message data with high confidentiality and integrity impact.

Affected Products

Quiet chat application versions 6.1.0-alpha.4 and below
Quiet backend/frontend communication API components
Deployments running pre-6.0.1 builds

Discovery Timeline

2025-07-24 - CVE-2025-53940 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-53940

Vulnerability Analysis

Quiet's API layer authenticates internal requests between the frontend and backend using a shared token. The token verification routine performed a byte-by-byte comparison that exited on the first mismatched character. This behavior leaks information through response latency because valid prefixes take measurably longer to reject than invalid ones. An attacker can iterate through candidate characters and measure response times to progressively reconstruct the full token.

Once the token is recovered, the attacker can invoke privileged API endpoints as if they were the legitimate frontend. This exposes confidential chat data, permits message manipulation, and can cascade into full compromise of the local Quiet instance.

Root Cause

The root cause is the use of a standard string or byte comparison operator instead of a constant-time comparison function such as crypto.timingSafeEqual in Node.js. Standard equality checks short-circuit on the first differing character, exposing partial-match information through timing side channels.

Attack Vector

The attack requires local access to the system running Quiet, where the attacker can send requests to the local API endpoint and precisely measure response times. The attacker sends a large volume of token guesses, statistically averages timing measurements to overcome network and scheduling noise, and identifies the character that produces the longest response time at each position. Repeating this per byte reconstructs the token without ever seeing it in cleartext.

No verified proof-of-concept code is publicly available. Refer to the GitHub Security Advisory and the GitHub Issue Discussion for technical details.

Detection Methods for CVE-2025-53940

Indicators of Compromise

High volumes of failed API authentication attempts against the local Quiet backend within a short time window
Sequential requests to the same authenticated endpoint with slowly varying token strings
Unusual local process activity making repeated loopback requests to Quiet's API port

Detection Strategies

Monitor Quiet backend logs for repeated 401/403 responses on token-authenticated endpoints originating from local processes
Correlate loopback network telemetry with process execution to identify non-frontend processes probing the Quiet API
Alert on statistical anomalies in request rates per source process against the Quiet backend

Monitoring Recommendations

Enable verbose authentication logging in Quiet and forward events to a centralized log platform for retention and analysis
Track process creation events on endpoints running Quiet to identify unauthorized tooling that could execute timing measurements
Baseline normal frontend-to-backend request patterns and alert on deviations such as burst request rates or non-standard user agents

How to Mitigate CVE-2025-53940

Immediate Actions Required

Upgrade Quiet to version 6.0.1 or later, which replaces the vulnerable comparison with a constant-time function
Inventory all endpoints running Quiet and confirm patched versions after upgrade
Restrict local access to systems running Quiet to trusted users only until patching is complete

Patch Information

The vulnerability is fixed in Quiet version 6.0.1. The fix replaces the insecure token comparison with a constant-time equality check. See the GitHub Pull Request for the code change and the GitHub Security Advisory for full remediation guidance.

Workarounds

Limit local user accounts on systems running vulnerable Quiet versions to reduce exposure to local attackers
Apply host-based firewall rules to restrict access to Quiet's local API port to authorized processes where feasible
Rotate any tokens or credentials used by Quiet after upgrading to invalidate values that may have been exposed

bash

# Upgrade Quiet to the patched release
npm install quiet@6.0.1

# Verify the installed version
npm ls quiet