# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **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 available:** No
- **Published:** 11 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** GHSA-r558-xpjx-65pf, UBUNTU-CVE-2026-124737

## 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 (Out-of-bounds Write)

## 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.

## Is CVE-2026-124737 being exploited?

There is no known exploitation of CVE-2026-124737 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-124737 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-124737 in the wild and no public exploit code.
Exposure: An affected version is only exploitable if your software uses the vulnerable function or option. Many projects that include it are not exposed.

Affected product: Red Hat Enterprise Linux 6. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-124737/ (Markdown: https://insights.sbomify.com/CVE-2026-124737/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-124737
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-124737
- OSV: https://osv.dev/vulnerability/CVE-2026-124737

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-124737/
Summaries are generated and may contain mistakes; the official description above is the record.