CVE-2026-124737 Busybox: heap buffer overflow in the tftp client on fallback to the default block size
A malicious TFTP server can overflow a heap buffer in BusyBox's TFTP client with a small block size, executing code or crashing it.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Harmful if only installed
- No
- Needs a specific call
- Yes
- Fix
- None listed
What is CVE-2026-124737?
CVE-2026-124737 is a high-severity memory corruption vulnerability in Red Hat Enterprise Linux 6, published on 11 Nov 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
A flaw was found in BusyBox. When the TFTP (Trivial File Transfer Protocol) client requests a custom small block size and receives a standard response, it falls back to the default block size without resizing the allocated memory buffer. A malicious TFTP server can exploit this issue by sending standard-sized network packets during a transfer, causing a heap buffer overflow. This flaw allows an attacker to achieve arbitrary code execution or cause a Denial of Service (DoS) by crashing the application.
Weakness: CWE-787
Which versions are affected by CVE-2026-124737?
An affected version is only exploitable if your software uses the vulnerable function or option. Many projects that include it are not exposed.
How do I fix CVE-2026-124737?
No fix has been published for CVE-2026-124737 yet. Limit exposure of the affected software until one is available.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-124737 being exploited?
There is no known exploitation of CVE-2026-124737 in the wild and no public exploit code.
Sources
Also known as GHSA-r558-xpjx-65pf, UBUNTU-CVE-2026-124737.