Read the docs
TI-2021-03098 Aliases CVE-2021-4239GHSA-6cr6-fmvc-vw2p

Weak encryption and denial of service in github.com/flynn/noise

Priority LOW 33CWE-311Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Information disclosure
Confidentiality · integrity · availability
None · High · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CISA ADP. Fix status from CNA and GitHub. Impact type from CWE-311.

Summary

The Noise protocol implementation suffers from weakened cryptographic security after encrypting 2^64 messages, and a potential denial of service attack. After 2^64 (~18.4 quintillion) messages are encrypted with the Encrypt function, the nonce counter will wrap around, causing multiple messages to be encrypted with the same key and nonce. In a separate issue, the Decrypt function increments the nonce state even when it fails to decrypt a message. If an attacker can provide an invalid input to the Decrypt function, this will cause the nonce state to desynchronize between the peers, resulting in a failure to encrypt all subsequent messages.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00378 31st percentileScored 2026-11-07
Fix Fixed github.com/flynn/noise (github.com/flynn/noise): 1.0.0github.com/flynn/noise (Go): 1.0.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
github.com/flynn/noisegithub.com/flynn/noisebefore 1.0.01.0.0Patch availableCNA
—github.com/flynn/noise (Go)before 1.0.01.0.0Patch availableGHSA-6cr6-fmvc-vw2p
  • github.com/flynn/noise Vendorgithub.com/flynn/noise Affected before 1.0.0 Fixed in 1.0.0 Patch available CNA
  • github.com/flynn/noise (Go) Vendor— Affected before 1.0.0 Fixed in 1.0.0 Patch available GHSA-6cr6-fmvc-vw2p

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:noiseprotocol:noise:-:*:*:*:*:go:*:*not specified by NVDVulnerableNoiseprotocol
  • cpe:2.3:a:noiseprotocol:noise:-:*:*:*:*:go:*:* Versions not specified by NVD Vulnerable ·Noiseprotocol

Remediation

  • Fix · CNA github.com/flynn/noise (github.com/flynn/noise) Fixed in 1.0.0
  • Fix · GHSA-6cr6-fmvc-vw2p github.com/flynn/noise (Go) Fixed in 1.0.0 Advisory →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-02 Threatist record created from CVE-2021-4239
  2. 2026-10-03 Alias added: GHSA-6cr6-fmvc-vw2p

References

Patch 2

Advisory 1

Other 2

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences