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Response snapshot Oct 27, 2026, 17:26 UTC

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VulnerabilityGHSA-c8m5-c952-6cm4

Rustls: Session Debug formatting exposes TLS master secrets and resumption PSKs

Formatting a client session value with Debug exposes its TLS 1.2 master secret or TLS 1.3 resumption PSK. A custom session store that logs these values can disclose keys to readers of the logs.

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-c8m5-c952-6cm4 (opens a new tab)

What happened

### Summary

Formatting a client session value with Debug exposes its TLS 1.2 master secret or TLS 1.3 resumption PSK. A custom session store that logs these values can disclose keys to readers of the logs. Ordinary connection and built-in cache diagnostics remain redacted, and the session-store interface already warns that its values are sensitive.

### Details

Derived formatters traverse the session's secret-bearing fields. This conflicts with the project's explicit [key-material redaction policy](https://github.com/rustls/rustls/blob/99f2358cae2954837dbb866faf6727de75489ab9/SECURITY.md#boundary-public-api).

Continue reading

### Proof of concept

Custom `ClientSessionStore` implementations could leak secret data by using the provided `Tls12ClientSessionValue` or `Tls13ClientSessionValue` in a way that triggers its implementation of the `Debug` trait.

### Impact

Such store implementations could leak the master secret for the TLS connection.

### 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-c8m5-c952-6cm4 (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-c8m5-c952-6cm4, 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: Session Debug formatting exposes TLS master secrets and resumption PSKs. https://kevwire.com/record/GHSA-c8m5-c952-6cm4

MLA

"Rustls: Session Debug formatting exposes TLS master secrets and resumption PSKs." KEVWire, 27 Oct. 2026, kevwire.com/record/GHSA-c8m5-c952-6cm4.

Chicago

KEVWire. "Rustls: Session Debug formatting exposes TLS master secrets and resumption PSKs." Last modified October 27, 2026. https://kevwire.com/record/GHSA-c8m5-c952-6cm4.

Evidence summary (plain text)

Rustls: Session Debug formatting exposes TLS master secrets and resumption PSKs (Oct 27, 2026).
Formatting a client session value with Debug exposes its TLS 1.2 master secret or TLS 1.3 resumption PSK. A custom session store that logs these values can disclose keys to readers of the logs. Ordinary connection and built-in cache diagnostics remain redacted, and the session-store interface already warns that its values are sensitive.

Derived formatters traverse the session's secret-bearing fields. This conflicts with the project's explicit [key-material redaction policy](https://github.com/rustls/rustls/blob/99f2358cae2954837dbb866faf6727de75489ab9/SECURITY.md#boundary-public-api).
Sources:
GitHub-reviewed advisory GHSA-c8m5-c952-6cm4: https://github.com/advisories/GHSA-c8m5-c952-6cm4
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-c8m5-c952-6cm4.
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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