Integer overflow in `hyper`'s parsing of the `Transfer-Encoding` header leads to data loss

When decoding chunk sizes that are too large, `hyper`'s code would encounter an integer overflow. Depending on the situation, this could lead to data loss from an incorrect total size, or in rarer cases, a request smuggling attack. To be vulnerable, you must be using `hyper` for any HTTP/1 purpose, including as a client or server, and consumers must send requests or responses that specify a chunk size greater than 18 exabytes. For a possible request smuggling attack to be possible, any upstream proxies must accept a chunk size greater than 64 bits.

Source published

7 Jul 2021 12:00:00 UTC

Source modified

12 Oct 2026 18:00:02 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H