CVE-2026-43798: A single crafted SSH message gives an unauthenticated network attacker an out-of-bounds stack write of attacker-controlled length and content against any application built on swift-nio-ssh. in Apple swift-nio-ssh

CVE-2026-43798 describes an out-of-bounds stack write vulnerability in Apple swift-nio-ssh. An unauthenticated attacker can send a specially crafted SSH message that triggers a stack write beyond intended bounds, with control over the length and content of the write. This affects all applications built on swift-nio-ssh versions before 0.14.1. The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow) and has a CVSS v3.1 score of 9.8, indicating critical severity. The issue is fixed in swift-nio-ssh version 0.14.1.

Successful exploitation allows an unauthenticated network attacker to execute an out-of-bounds stack write, potentially leading to arbitrary code execution, complete compromise of confidentiality, integrity, and availability of the affected application. This can result in full system compromise of any application using vulnerable versions of swift-nio-ssh.

Upgrade all affected applications to swift-nio-ssh version 0.14.1 or later, where this vulnerability has been fixed. No other mitigations are indicated or necessary once the update is applied.