CVE-2024-45719: Predictable Authorization Token Vulnerability in Apache Answer
Overview
CVE-20240-45719
highlights a critical vulnerability in Apache Answer, where UUID Version 1 (UUIDv1) is used as an authorization token. Due to the predictable nature of UUIDv1, attackers can predict and brute force valid tokens, enabling session hijacking and unauthorized access to user accounts.
This vulnerability has been validated through real-world testing, demonstrating that an attacker with minimal privileges can exploit this flaw to hijack future user sessions at scale. Immediate remediation is essential to protect user accounts and system integrity.
Affected systems
All instances of Apache Answer where UUIDv1 is used as an authorization token are affected. This includes systems that rely on UUIDv1 for identifying and validating user sessions.
Technical Details
In the Apache Answer codebase, UUIDv1 is used for generating authorization tokens. Below is an example of the relevant code, which demonstrates the usage of UUIDv1:
Here, the uuid.NewUUID()
function generates a UUID Version 1 token. While this ensures uniqueness, it lacks the cryptographic randomness required for security-critical use cases, such as session management or authorization.
UUIDv1 Breakdown
Implementation
- Reference: https://github.com/google/uuid/blob/master/version1.go
UUID Version 1 is structured as follows:
- Timestamp (60 bits): Represents the number of 100-nanosecond intervals since October 15, 1582, derived directly from the system clock.
- Clock Sequence (14 bits): Used to avoid duplicates within the same timestamp. However, it is relatively static unless the system clock changes or the server restarts.
- Node Identifier (48 bits): Typically derived from the server’s MAC address, making it constant for the machine.
Example UUID Analysis
Given the UUID 70935f8d-6b50-11ef-9728-0242ac110002, the components can be broken down as follows:
70935f8d
: Timestamp (lower 32 bits).6b50
: Timestamp (middle 16 bits).11ef
: Timestamp (upper 12 bits), combined with the version (1).9728
: Clock sequence, which remains static across multiple tokens generated at the same time.0242ac110002
: Node identifier (MAC address or equivalent).
This predictable structure makes it possible for attackers to predict future tokens after capturing one valid UUID.
Attack Scenario
Step 1: Obtain a Valid UUID Token
An attacker begins by obtaining a valid UUIDv1 authorization token. This can be achieved by:
- Signing up for a low-privileged account.
- Intercepting network traffic or logs containing tokens.
- Example captured token:
70935f8d-6b50-11ef-9728-0242ac110002
Step 2: Extract Predictable Components
- The attacker extracts:
Clock Sequence: 9728
Node Identifier: 0242ac110002
- These components remain constant for the server, enabling the attacker to focus on brute-forcing the timestamp.
Step 3: Brute Force Future Tokens
The attacker writes a script to iterate over possible timestamps while keeping the clock sequence and node identifier constant. The following Python script demonstrates this approach:
Real-World Feasibility
For testing purposes, I used a 1-minute timestamp range. On a 32-core, 64GB RAM virtual machine, the script generated a valid token in 2-3 minutes. In real-world scenarios, the script can run continuously, capturing all future valid tokens generated by the system.
Even if the server updates the clock sequence or node identifier, the attacker can simply capture a new token from their account and continue the attack.
The attacker uses the generated tokens to send requests to the web application. For example:
GET /answer/api/v1/notification/page?type=achievement&page=1&page_size=10 HTTP/1.1
Host: localhost:9080
Authorization: <Generated-UUID>
A 200 OK
response confirms session hijacking.
Resolution and Recommendations
The Apache Answer maintainers have addressed this vulnerability by upgrading the token generation mechanism in version 1.4.1
. Users are strongly advised to update their installations to Apache Answer 1.4.1
to mitigate the risk of account takeover.