HTTP Request Smuggling Affecting h11 package, versions [,0.16.0)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published3 Jun 2025
- disclosed24 Apr 2025
- creditJeppe Bonde Weikop
Introduced: 24 Apr 2025
CVE-2025-43859 (opens in a new tab)How to fix?
Upgrade h11 to version 0.16.0 or higher.
Overview
h11 is an A pure-Python, bring-your-own-I/O implementation of HTTP/1.1
Affected versions of this package are vulnerable to HTTP Request Smuggling via the class ChunkedReader in _readers.py file, which performs the parsing of line terminators in chunked-coding message bodies. An attacker can exploit this to bypass security controls and smuggle HTTP requests by crafting malformed chunked-encoding bodies.