GHSA-h2v8-394m-p7vv

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GHSA-h2v8-394m-p7vv

Summary: Rustls: Brotli certificate decompression can allocate an attacker-controlled amount of memory up to 1 GiB before authentication.

Details: ### Summary The built-in (but disabled by default) Brotli certificate decoder bounds the output buffer but accepts an input-selected history window. A header of five bytes can specify a 1 GiB window allocation. A peer can abort a process whose allocator cannot satisfy that request. A client must enable Brotli and connect to the peer; a server must enable Brotli and request a client certificate. Neither direction requires a trusted attacker certificate. ### Details rustls calls `BrotliDecompress` which enables Brotli's large-window extension. rustls applies a limit to certificates, but this applies to the decompressed result, and not to any internal allocations the process requires. ### Impact Client applications that enable the `brotli` feature will be vulnerable to malicious servers. Server applications that enable the `brotli` feature and enable client authentication will be vulnerable to malicious clients. Potential for denial of service due to memory exhaustion from peers sending malicious Brotli-encoded certificates, for applications that enable Brotli decompression. ### Acknowledgement Thanks to OpenAI [[email protected]](mailto:[email protected]) for the disclosure.

References: https://github.com/rustls/rustls/security/advisories/GHSA-h2v8-394m-p7vv, https://github.com/rustls/rustls/pull/3297, https://github.com/rustls/rustls/pull/3354, https://github.com/rustls/rustls/commit/1aa987af37d0d79b98781d345895ac0059ce345c, https://github.com/rustls/rustls/commit/402b7b78b7ae87d59e19cf07ee07f3fc19e6537e, https://github.com/rustls/rustls, https://github.com/rustls/rustls/releases/tag/v/0.23.46, https://rustsec.org/advisories/RUSTSEC-2026-0348.html