# CVE-2026-123609: Rustls session Debug formatting exposes TLS secret keys

Source: https://junglewise.ai/threats/cve-2026-123609-rustls-before-0-23-46-and-0-24-0-dev-1-before-0-24-0-dev-2  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-08. Updated: 2026-11-08  
License: CC BY 4.0 with a link back

CVE-2026-123609 · Severity: medium · CVSS 4 · Published 2026-11-08

Rustls is a TLS library used to encrypt network communications. When application developers use custom logging with Rustls session data, the Debug formatting accidentally exposes sensitive cryptographic keys (TLS master secrets and resumption keys) to anyone reading the logs. This only affects custom implementations that specifically log session values, not normal Rustls usage.

Technologies: [Rustls](https://junglewise.ai/threats/technologies/rustls-rustls). Vendors: [Rustls](https://junglewise.ai/threats/vendors/rustls).

## Quick answers

**Is CVE-2026-123609 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-123609 being exploited in the wild.

**How severe is CVE-2026-123609?** Medium severity, with a CVSS score of 4, published 8 November 2026.

**Which products and versions are affected?** Rustls before 0.23.46 and 0.24.0-dev.1 before 0.24.0-dev.2.

**Is there a fix for CVE-2026-123609?** Yes: fixed in Rustls 0.23.46, 0.24.0-dev.2 and later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-123609 attacked?** It is attacked with local access.

**Am I affected by CVE-2026-123609?** Check whether you run Rustls at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in Rustls 0.23.46, 0.24.0-dev.2 and later

## Technical details

The vulnerability stems from derived Debug trait implementations on Tls12ClientSessionValue and Tls13ClientSessionValue that expose secret key material (TLS 1.2 master secrets and TLS 1.3 resumption PSKs). Custom ClientSessionStore implementations that log these session values will leak these secrets. The attack requires local access and a developer-written logging implementation that uses Debug formatting on session objects.

## Affected products

- Rustls Rustls before 0.23.46 and 0.24.0-dev.1 before 0.24.0-dev.2

## Timeline

- 2026-10-14: disclosed
- 2026-11-08: advisory

## References

- [https://github.com/rustls/rustls/security/advisories/GHSA-c8m5-c952-6cm4](https://github.com/rustls/rustls/security/advisories/GHSA-c8m5-c952-6cm4)
- [https://www.vulncheck.com/advisories/rustls-before-0.23.46-and-0.24.0-dev.1-before-0.24.0-dev.2-secret-exposure-via-debug](https://www.vulncheck.com/advisories/rustls-before-0.23.46-and-0.24.0-dev.1-before-0.24.0-dev.2-secret-exposure-via-debug)

## Related threats

- [Rustls TLS 1.3 handshake message encryption level bypass](https://junglewise.ai/threats/cve-2026-123613-rustls-from-0-23-13-before-0-23-45-accepts-tls-1-3-handshake)
- [Rustls client session debug formatting information disclosure](https://junglewise.ai/threats/rustls-session-debug-formatting-exposes-tls-master-secrets-and-6519d2da)
- [Rustls TLS 1.3 handshake message validation bypass across encryption levels](https://junglewise.ai/threats/rustls-tls-1-3-handshake-messages-incorrectly-accepted-across-4eccbdca)