Credential disclosure via retained cross-origin redirect headers
Published Apr 1, 2026 · Updated Apr 1, 2026
Information disclosure in aio-libs aiohttp before 3.13.4 allows remote attackers to receive sensitive headers through cross-origin redirects. In ClientSession redirect handling in aiohttp/client.py, an origin change cleared Authorization but forwarded Cookie and Proxy-Authorization headers to the new origin. Exploitation requires an application to follow an attacker-controlled redirect while sending those headers, exposing their contents to the destination.
Summary
What happened
Information disclosure in aio-libs aiohttp before 3.13.4 allows remote attackers to receive sensitive headers through cross-origin redirects. In ClientSession redirect handling in aiohttp/client.py, an origin change cleared Authorization but forwarded Cookie and Proxy-Authorization headers to the new origin. Exploitation requires an application to follow an attacker-controlled redirect while sending those headers, exposing their contents to the destination.
The record
- CVE
- CVE-2026-34518
- Published
- Apr 1, 2026
- Updated
- Apr 1, 2026
- Vendor
- aio-libs
- Product
- aiohttp
- Classifications
- CWE-200, T1539
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 1, 2026CVE publishedPublication date reported by the CVE source.
- Apr 1, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=< 3.13.4
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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