An issue was discovered in the http crate before 0.1.20 for Rust. An integer overflow in HeaderMap::reserve() could result in denial of service (e.g., an infinite loop).

Affected: crates.io: http

HeaderMap::reserve() used usize::next_power_of_two() to calculate the increased capacity. However, next_power_of_two() silently overflows to 0 if given a sufficiently large number in release mode.

If the map was not empty when the overflow happens, the library will invoke self.grow(0) and start infinite probing. This allows an attacker who controls the argument to reserve() to cause a potential denial of service (DoS).

The flaw was corrected in 0.1.20 release of http crate.

Affected: crates.io: http

`HeaderMap::reserve()` used `usize::next_power_of_two()` to calculate the increased capacity. However, `next_power_of_two()` silently overflows to 0 if given a sufficiently large number in release mode.

If the map was not empty when the overflow happens, the library will invoke `self.grow(0)` and start infinite probing. This allows an attacker who controls the argument to `reserve()` to cause a potential denial of service (DoS).

The flaw was corrected in 0.1.20 release of `http` crate.

Affected: Ubuntu:20.04:LTS: rust-http, Ubuntu:24.04:LTS: rust-http, Ubuntu:25.10: rust-http, Ubuntu:26.04:LTS: rust-http

An issue was discovered in the http crate before 0.1.20 for Rust. An integer overflow in HeaderMap::reserve() could result in denial of service (e.g., an infinite loop).