CVE-2018-6596 in AnyMail
Summary
by MITRE
webhooks/base.py in Anymail (aka django-anymail) before 1.2.1 is prone to a timing attack vulnerability on the WEBHOOK_AUTHORIZATION secret, which allows remote attackers to post arbitrary e-mail tracking events.
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Analysis
by VulDB Data Team • 02/03/2023
The vulnerability identified as CVE-2018-6596 affects Anymail, a django package that provides email backend functionality for sending and receiving emails through various email service providers. This specific flaw exists in the webhooks/base.py file and impacts versions prior to 1.2.1, creating a significant security risk for applications that rely on email tracking and webhook processing. The vulnerability stems from improper handling of authentication secrets during webhook validation processes, exposing applications to potential exploitation by malicious actors who can manipulate email tracking events.
The technical implementation flaw involves a timing attack vulnerability in the WEBHOOK_AUTHORIZATION secret validation mechanism. When processing incoming webhook requests, the system performs a comparison operation between the provided authorization header and the expected secret value. This comparison operation does not use constant-time string comparison methods, which allows attackers to measure response times and infer information about the correct secret through statistical analysis. The timing differences in the comparison process create observable variations that can be exploited to gradually deduce the correct authorization secret through repeated requests and timing measurements.
This vulnerability operates at the application layer and specifically targets the authentication validation process within the email tracking webhook system. The operational impact is substantial as it allows remote attackers to forge legitimate webhook requests that appear to originate from authorized email service providers. Attackers can exploit this weakness to post arbitrary email tracking events such as opens, clicks, bounces, and unsubscribes, potentially leading to data manipulation, false reporting, and unauthorized access to email analytics. The vulnerability is particularly dangerous in environments where webhook authentication is critical for maintaining the integrity of email tracking data and preventing unauthorized modifications to email campaign metrics.
The security implications extend beyond simple data manipulation to include potential system compromise and data integrity violations. Organizations using Anymail for email tracking and analytics are at risk of having their email campaign data corrupted or falsified, which could impact marketing decisions, customer behavior analysis, and business intelligence derived from email engagement metrics. The vulnerability also aligns with CWE-203, which describes "Observable Timing Discrepancy" in security contexts, and represents a classic example of how timing attacks can be leveraged to bypass authentication mechanisms. According to ATT&CK framework, this vulnerability maps to T1213.002 - "Data from Information Repositories" and T1190 - "Exploit Public-Facing Application" as attackers can exploit the publicly accessible webhook endpoints to gain unauthorized access to email tracking data.
The recommended mitigation strategy involves upgrading to Anymail version 1.2.1 or later, which implements proper constant-time string comparison methods to prevent timing attacks. Organizations should also implement additional security measures such as rate limiting on webhook endpoints, monitoring for unusual webhook activity patterns, and ensuring that webhook secrets are properly rotated. Network-level protections including firewall rules restricting webhook endpoint access and intrusion detection systems monitoring for timing-based attack patterns can provide additional defense layers. Security teams should conduct comprehensive vulnerability assessments to identify all instances of affected Anymail installations within their infrastructure and ensure that proper access controls are in place to limit exposure of webhook endpoints to unauthorized parties.