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High severityNVD Advisory· Published Sep 6, 2022· Updated Aug 4, 2024

CVE-2021-43565

CVE-2021-43565

Description

The x/crypto/ssh package before 0.0.0-20211202192323-5770296d904e of golang.org/x/crypto allows an attacker to panic an SSH server.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

Unauthenticated clients can panic Go SSH servers by sending a malformed packet with empty plaintext, leading to denial of service.

Vulnerability

Description

The vulnerability resides in the golang.org/x/crypto/ssh package before version v0.0.0-20211202192323-5770296d904e. When using AES-GCM or ChaCha20Poly1305 encryption modes, the SSH server assumes that a decrypted packet will always contain at least one byte (the padding length). A specially crafted packet with empty plaintext violates this assumption, causing a nil pointer dereference or index-out-of-range panic [3][4].

Exploitation

An unauthenticated attacker can trigger the panic by sending a malformed SSH transport layer packet during the key exchange or any subsequent encrypted phase. No prior authentication or special network position is required; the attacker only needs to establish a TCP connection to the SSH server and send the crafted packet [3].

Impact

Successful exploitation results in a panic of the SSH server process, leading to a denial of service (DoS). The server becomes unavailable for legitimate connections until restarted. Since the panic occurs before any authentication, the attack can be launched by any client that can reach the SSH port [3][4].

Mitigation

The fix was released in commit 5770296d904e and is included in golang.org/x/crypto version v0.0.0-20211202192323-5770296d904e and later. Users should update their dependency to this version or newer. The Go security team has also published a vulnerability entry (GO-2022-0968) tracking this issue [2][3].

References
  1. GO-2022-0968 - Go Packages
  2. [security] Vulnerability in golang.org/x/crypto/ssh
  3. x/crypto/ssh: empty plaintext packet causes panic

AI Insight generated on May 21, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
golang.org/x/cryptoGo
< 0.0.0-20211202192323-5770296d904e0.0.0-20211202192323-5770296d904e

Affected products

142

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

References

8

News mentions

0

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