CVE-2026-42859 Neat VNC: Buffer overflow due to oversized RSA public keys
An unauthenticated remote attacker can crash the VNC server by sending oversized RSA public keys, causing a stack buffer overflow.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-42859?
CVE-2026-42859 is a high-severity memory corruption vulnerability in any1 neatvnc, published on 11 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Neat VNC is a VNC server library. Prior to 0.9.6, a pre-authentication stack buffer overflow exists in neatvnc in the RSA-AES security type handler. An unauthenticated remote attacker who can reach the VNC listening socket can send a crafted security type 5 (RSA-AES) or security type 129 (RSA-AES-256) handshake with an oversized client RSA public key, causing rsa_aes_send_challenge in src/auth/rsa-aes.c to overflow a 1024-byte on-stack buffer when encrypting the server challenge. This results in at least a denial of service via server crash. This vulnerability is fixed in 0.9.6.
Weakness: CWE-120
Which versions are affected by CVE-2026-42859?
How do I fix CVE-2026-42859?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-42859 being exploited?
There is no known exploitation of CVE-2026-42859 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2026-42859, GHSA-567c-gpv8-qh9h, UBUNTU-CVE-2026-42859.