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Response snapshot Oct 27, 2026, 17:26 UTC

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VulnerabilityGHSA-h2v8-394m-p7vv

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

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.

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: rustls: 0.23.46; rustls: 0.24.0-dev.2. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-h2v8-394m-p7vv (opens a new tab)

What happened

### 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.

Continue reading

### 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 [OutboundDisclosures@openai.com](mailto:OutboundDisclosures@openai.com) for the disclosure.

Affected package ranges reported by GitHub: rustls: < 0.23.46 rustls: >= 0.24.0-dev.1, < 0.24.0-dev.2

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-h2v8-394m-p7vv (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-h2v8-394m-p7vv, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). Rustls: Brotli certificate decompression can allocate an attacker-controlled amount of memory up to 1 GiB before authentication.. https://kevwire.com/record/GHSA-h2v8-394m-p7vv

MLA

"Rustls: Brotli certificate decompression can allocate an attacker-controlled amount of memory up to 1 GiB before authentication.." KEVWire, 27 Oct. 2026, kevwire.com/record/GHSA-h2v8-394m-p7vv.

Chicago

KEVWire. "Rustls: Brotli certificate decompression can allocate an attacker-controlled amount of memory up to 1 GiB before authentication.." Last modified October 27, 2026. https://kevwire.com/record/GHSA-h2v8-394m-p7vv.

Evidence summary (plain text)

Rustls: Brotli certificate decompression can allocate an attacker-controlled amount of memory up to 1 GiB before authentication. (Oct 27, 2026).
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.

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.
Sources:
GitHub-reviewed advisory GHSA-h2v8-394m-p7vv: https://github.com/advisories/GHSA-h2v8-394m-p7vv
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-h2v8-394m-p7vv.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 17:25 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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