CVE-2021-43565Network attack vector

Unauthenticated SSH server crash via empty plaintext

Published Sep 6, 2022 · Updated Aug 4, 2024

Improper packet validation in golang.org/x/crypto/ssh before 0.0.0-20211202192323-5770296d904e allows remote attackers to crash SSH servers. The AES-GCM and ChaCha20-Poly1305 packet readers index the first plaintext byte for padding without first rejecting a decrypted zero-length payload. Remote attackers need no authentication but must negotiate one of those ciphers and deliver a malformed encrypted packet; the resulting panic can terminate the hosting process and interrupt service.

CVSS severity7.5
High
EPSS probability1.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper packet validation in golang.org/x/crypto/ssh before 0.0.0-20211202192323-5770296d904e allows remote attackers to crash SSH servers. The AES-GCM and ChaCha20-Poly1305 packet readers index the first plaintext byte for padding without first rejecting a decrypted zero-length payload. Remote attackers need no authentication but must negotiate one of those ciphers and deliver a malformed encrypted packet; the resulting panic can terminate the hosting process and interrupt service.

The record

CVE
CVE-2021-43565
Published
Sep 6, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 6, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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