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.
> Brotli certificate decompression can allocate up to 1 GiB before authentication
| Details | |
| ------------------- | ---------------------------------------------- |
| Package | `rustls` |
| Version | `0.23.45` |
| URL | [https://github.com/rustls/rustls/pull/3297](https://github.com/rustls/rustls/pull/3297) |
| Date | 2026-10-14 |
| Patched versions | `>=0.23.46` |
| Unaffected versions | `<0.23.9` |
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.
See [advisory page](https://rustsec.org/advisories/RUSTSEC-2026-0348.html) for additional details.
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rustls0.23.45>=0.23.46<0.23.9The built-in Brotli certificate decompressor (enabled by the non-default
brotlicrate feature) bounded the size of the decompressed output, butaccepted 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:
brotlifeature and connect to a malicious server, andbrotlifeature and request client certificates.Applications that do not enable the
brotlifeature are not affected.See advisory page for additional details.