RUSTSEC-2026-0348: Brotli certificate decompression can allocate up to 1 GiB before authentication #3485

The built-in Brotli certificate decompressor (enabled by the non-default
brotli crate feature) bounded the size of the decompressed output, but
accepted a peer-selected history window. Brotli's large-window extension was
enabled, so a five-byte header could cause an allocation of 1 GiB. A peer can
abort a process whose allocator cannot satisfy that request.

No trusted certificate is required by the attacker. Affected configurations are:

• clients that enable the brotli feature and connect to a malicious server, and
• servers that enable the brotli feature and request client certificates.

Applications that do not enable the brotli feature are not affected.