CVE-2026-5774 Overview
CVE-2026-5774 is a race condition vulnerability affecting Canonical Juju, a popular open-source application modeling tool used for deploying, configuring, and managing applications across multiple cloud platforms. The vulnerability stems from improper synchronization of the userTokens map in the API server, which may allow an authenticated user to cause a denial of service on the server or potentially reuse a single-use discharge token.
Critical Impact
Authenticated attackers can exploit this race condition to disrupt Juju API server availability or potentially bypass single-use token protections, affecting infrastructure management operations.
Affected Products
- Canonical Juju 4.0.5
- Canonical Juju 3.6.20
- Canonical Juju 2.9.56
Discovery Timeline
- 2026-04-10 - CVE-2026-5774 published to NVD
- 2026-04-13 - Last updated in NVD database
Technical Details for CVE-2026-5774
Vulnerability Analysis
This vulnerability is classified under CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization), commonly known as a race condition. The flaw exists within the Juju API server's handling of the userTokens map, a shared resource that manages authentication tokens for connected users.
When multiple API requests attempt to access or modify the userTokens map concurrently without proper synchronization primitives (such as mutexes or read-write locks), the system becomes susceptible to race conditions. This can result in two primary impacts: first, the API server may crash or become unresponsive due to corrupted state, leading to a denial of service condition; second, timing-based exploitation could potentially allow an attacker to reuse a discharge token that was intended for single use only.
The network-based attack vector requires authentication, limiting exploitation to users who already have valid credentials to the Juju controller. However, in multi-tenant or shared environments, this could allow a malicious authenticated user to impact the availability of the management plane for other legitimate users.
Root Cause
The root cause of this vulnerability is the absence of proper synchronization mechanisms when accessing the userTokens map in the Juju API server. In Go, maps are not safe for concurrent use without explicit synchronization. When multiple goroutines access the map simultaneously—particularly when at least one is writing—undefined behavior can occur, including data corruption, panics, or inconsistent reads.
The userTokens map likely stores discharge tokens used in Macaroon-based authentication, where single-use tokens are critical for preventing replay attacks. Without proper locking, the check-then-use pattern for these tokens becomes vulnerable to time-of-check time-of-use (TOCTOU) conditions.
Attack Vector
The vulnerability is exploitable over the network by authenticated users. An attacker would need valid credentials to the Juju controller to exploit this flaw. The attack scenario involves sending concurrent API requests designed to trigger race conditions in the token handling code.
The exploitation mechanism involves timing-based attacks where an attacker sends multiple simultaneous requests that interact with the userTokens map. Due to the lack of synchronization, there's a window where a single-use token could be validated multiple times before being invalidated, or where concurrent modifications could cause the server to panic.
For detailed technical analysis and the actual fix implementation, refer to the GitHub Security Advisory GHSA-7m55-2hr4-pw78 and the associated pull requests #22205 and #22206.
Detection Methods for CVE-2026-5774
Indicators of Compromise
- Unexpected Juju API server crashes or restarts, particularly with panic messages related to concurrent map access
- Anomalous spikes in authentication-related API requests from single users
- Log entries indicating token reuse or authentication anomalies
- Multiple simultaneous connections from the same user performing rapid token operations
Detection Strategies
- Monitor Juju controller logs for Go runtime panics related to concurrent map writes
- Implement alerting for unusual patterns of API authentication failures or token validation errors
- Deploy network monitoring to detect high-frequency API request patterns that could indicate exploitation attempts
- Review audit logs for evidence of discharge token reuse across multiple sessions
Monitoring Recommendations
- Enable verbose logging on Juju controllers to capture detailed authentication flow information
- Set up application performance monitoring (APM) to detect latency spikes or error rate increases in the API server
- Configure process monitoring to alert on unexpected Juju controller restarts
- Implement rate limiting on authentication endpoints to reduce the attack surface for race condition exploitation
How to Mitigate CVE-2026-5774
Immediate Actions Required
- Identify all Juju deployments running affected versions (4.0.5, 3.6.20, or 2.9.56)
- Review the security advisory and apply the patches from the referenced pull requests
- Restrict network access to Juju controllers to trusted networks only
- Implement additional authentication controls and monitoring while awaiting patch deployment
Patch Information
Canonical has addressed this vulnerability through pull requests #22205 and #22206. These patches introduce proper synchronization mechanisms to the userTokens map handling in the API server. Organizations should upgrade to patched versions of Juju as soon as they become available through official Canonical channels.
For detailed patch information and upgrade instructions, consult the GitHub Security Advisory GHSA-7m55-2hr4-pw78.
Workarounds
- Implement network-level access controls to limit which users and systems can reach the Juju API server
- Deploy a reverse proxy with rate limiting in front of the Juju controller to reduce concurrent request volume
- Monitor and alert on authentication anomalies to detect potential exploitation attempts
- Consider temporarily restricting API access to essential operations only until patches can be applied
# Example: Restrict Juju API access using firewall rules
# Limit access to Juju controller port (default 17070) to trusted networks
sudo ufw allow from 10.0.0.0/8 to any port 17070
sudo ufw deny 17070
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
