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CVE-2026-55200 is a critical client-side memory corruption vulnerability in libssh2 affecting versions through 1.11.1. The flaw is in ssh2_transport_read() in transport.c, where an attacker-controlled SSH packet_length field is not subjected to a proper upper-bound check before being used in size arithmetic. A sufficiently large packet_length value can trigger integer wraparound, resulting in an undersized heap allocation followed by an out-of-bounds write when packet data is processed. Because the vulnerable logic is reached while parsing transport-layer SSH packets, exploitation is possible before authentication completes. A malicious or compromised SSH server can therefore trigger heap corruption in a connecting libssh2-based client and potentially achieve arbitrary code execution.
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2 valid exploits after Mallory filtered fakes, detection scripts, and README-only repos (1 hidden).
Repository contains a single C proof-of-concept exploit and a README. The main file, CVE-2026-55200.c, implements a multithreaded TCP server that impersonates an SSH service. For each inbound client connection, it sends a fake SSH banner, receives the client's banner, sends a minimal fake SSH_MSG_KEXINIT packet, receives additional client handshake data, and then transmits a malformed packet with packet_length set to 0xFFFFFFFF and a body filled largely with 0x41 bytes. The stated goal is to trigger an out-of-bounds write / heap corruption condition in libssh2 clients <= 1.11.1 during pre-authentication packet parsing. This is a server-side lure exploit against connecting clients, not an exploit against an SSH server. No shellcode, command execution, or post-exploitation logic is included, so the repository is best classified as a proof of concept intended to demonstrate crash or memory corruption potential. The README provides vulnerability background, impact claims, mitigation guidance, and references, but the actionable exploit logic is entirely in the single C source file.
This repository is a small standalone proof-of-concept exploit consisting of one C source file and a README. The main file, CVE-2026-55200.c, implements a multithreaded malicious SSH server that listens on a configurable TCP port (default 2222), accepts inbound client connections, performs a minimal SSH-like handshake, and then sends a crafted packet designed to trigger an out-of-bounds write in vulnerable libssh2 clients. The exploit flow is: send attacker-controlled SSH banner, receive client banner, send a fake SSH_MSG_KEXINIT structure, receive client key-exchange data, then transmit a malicious packet with packet_length set to 0xFFFFFFFF and a body filled largely with 0x41 bytes. The code uses pthreads to handle multiple clients concurrently and basic socket APIs for bind/listen/accept/send/recv. The README documents the claimed target as libssh2 <= 1.11.1 and describes the vulnerability as a network-reachable packet length validation flaw in SSH transport processing. There is no post-exploitation logic, shell payload, callback infrastructure, or framework integration; the repository is focused purely on triggering memory corruption/DoS and potentially enabling further exploitation research.
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140 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An out-of-bounds write vulnerability in libssh2's ssh2_transport_read function that can be triggered pre-authentication and may enable remote code execution against vulnerable clients.
A pre-authentication out-of-bounds write vulnerability in libssh2's ssh2_transport_read() caused by improper validation of the SSH packet_length field, enabling undersized heap allocation and subsequent heap overwrite during transport-layer packet parsing.
Critical out-of-bounds write vulnerability in libssh2 caused by an integer overflow leading to a buffer overflow in ssh2_transport_read(), potentially enabling unauthenticated remote code execution via crafted SSH packets.
A severe pre-authentication remote code execution vulnerability in libssh2 caused by specially crafted SSH packets with oversized packet_length values that manipulate heap memory.
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