Open Redirect in WebOb HTTP Header Handling

Impact Analysis

This vulnerability can lead to open redirect attacks, where an attacker can redirect users from a trusted site to a malicious external site.

Such redirects can be used for phishing, stealing user credentials, or distributing malware by making users believe they are navigating within a legitimate site.

Because the vulnerability requires user interaction (UI:R) and can be exploited remotely (AV:N) without privileges (PR:N), it poses a moderate risk.

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Mitigation Strategies

The vulnerability is fixed in WebOb version 1.8.10. To mitigate this vulnerability, you should upgrade WebOb to version 1.8.10 or later.

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Executive Summary

This vulnerability exists in WebOb versions prior to 1.8.10 and involves the normalization of the HTTP Location header during redirects. WebOb uses Python's urljoin to combine the redirect target with the request URI. Since Python 3.10, urlsplit strips certain ASCII characters (tab, carriage return, newline) before parsing, which can cause a redirect target containing these characters to be interpreted as a protocol-relative URL pointing to an attacker-controlled host. This allows an attacker who can influence the redirect location to redirect users to arbitrary external sites instead of the intended destination.

The vulnerability bypasses a previous fix (CVE-2024-42353) that escaped leading double slashes, making it possible to exploit open redirects through crafted redirect targets.

This issue is fixed in WebOb version 1.8.10.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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Detection Guidance

This vulnerability involves an open redirect caused by improper normalization of the HTTP Location header during redirects in WebOb versions prior to 1.8.10.

To detect this vulnerability on your system or network, you can monitor HTTP responses for redirect Location headers that contain suspicious characters such as ASCII tab (\t), carriage return, or newline characters, or that result in protocol-relative URLs (starting with //) pointing to external or attacker-controlled hosts.

Suggested commands to help detect potential exploitation attempts include using tools like curl or grep to inspect HTTP responses for unusual redirect Location headers.

• Use curl to follow redirects and show the Location header: curl -I -L http://your-target-url
• Search logs or captured HTTP traffic for Location headers containing suspicious characters or protocol-relative URLs, for example using grep: grep -P 'Location:.*(\t|\r|\n|//)' access.log
• Use network traffic analysis tools (e.g., Wireshark or tcpdump) to capture HTTP responses and filter for Location headers with unusual redirect targets.

Additionally, ensure your WebOb library is updated to version 1.8.10 or later to mitigate this vulnerability.

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