CVE-2026-54770: WebOb: Open redirect in Location header normalization via leading C0 control / space characters
WebOb provides objects for HTTP requests and responses. Prior to 1.8.11, Response.makelocationabsolute() in src/webob/response.py checks a Location value for a URI scheme or leading double slash before urllib.parse.urljoin() strips leading C0 control characters and spaces. An attacker-controlled value such as a space followed by a protocol-relative or absolute URL can therefore bypass SCHEMERE and startswith("//") checks and be normalized to an off-host redirect. Request.relativeurl() and webob.exc.HTTPMove subclasses, including HTTPFound, are also affected because they use the same unsafe URL joining behavior or bypass the earlier normalization path. An unauthenticated attacker who can influence an application's redirect target can send users to an attacker-controlled host for phishing or OAuth and SSO token theft, but exploitation requires the user to follow the redirect. This issue is fixed in version 1.8.11.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
WebObto a version that resolves this vulnerability.Fixed in 1.8.11
Event History
Frequently Asked Questions
Which application flows should be reviewed?
Review flows where an unauthenticated user can influence a redirect target, particularly those using Response location handling, Request.relative_url(), or webob.exc._HTTPMove subclasses such as HTTPFound. Values beginning with C0 control characters or spaces before an absolute or protocol-relative URL are relevant test cases.
What does an attacker need to exploit this issue?
The attacker needs to control or influence an application's redirect target. No authentication is required, but the victim must follow the resulting redirect.
What version resolves the issue?
The issue is fixed in WebOb 1.8.11. Versions prior to 1.8.11 are affected.