# CVE-2026-38638: relibc index out of bounds in with_argv

Source: https://junglewise.ai/threats/cve-2026-38638-relibc-index-out-of-bounds-in-with-argv  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-08-28. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2026-38638 · Severity: high · CVSS 7.5 · Published 2026-08-28

relibc is a C standard library implementation used by the Redox operating system. A flaw in the execl() function allows a local attacker to crash processes by passing an excessive number of arguments, resulting in denial of service.

Technologies: [Redox OS Relibc](https://junglewise.ai/threats/technologies/relibc). Vendors: [Redox OS](https://junglewise.ai/threats/vendors/redox-os).

## Quick answers

**Is CVE-2026-38638 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-38638 being exploited in the wild.

**How severe is CVE-2026-38638?** High severity, with a CVSS score of 7.5, published 28 August 2026.

**Which products and versions are affected?** Redox OS Relibc commit 61f42d and earlier.

**Is there a fix for CVE-2026-38638?** A patch was published on 2026: Fix available in merge request 989 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-38638 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-38638?** Check whether you run Redox OS Relibc at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An index out of bounds vulnerability exists in the with_argv function (src/header/unistd/mod.rs) when handling execl() calls with many arguments. The vulnerable code writes to out[argc] without verifying that argc fits within the allocated buffer bounds. The attack is local: an attacker executes a program that calls execl() with over 100 arguments, triggering a buffer overflow that causes an invalid opcode fault and kernel panic. A fix is available in merge request 989 at the relibc repository.

## Affected products

- Redox OS relibc commit 61f42d and earlier

## Timeline

- 2026-08-28: disclosed
- 2026: patched: Fix available in merge request 989

## References

- [https://github.com/Marsman1996/pocs/tree/master/redox/CVE-2026-38638](https://github.com/Marsman1996/pocs/tree/master/redox/CVE-2026-38638)
- [https://gitlab.redox-os.org/redox-os/relibc/-/issues/261](https://gitlab.redox-os.org/redox-os/relibc/-/issues/261)

## Related threats

- [relibc seekdir() denial of service via invalid offset](https://junglewise.ai/threats/cve-2026-38636-relibc-seekdir-denial-of-service-via-invalid-offset)
- [Redox OS relibc denial of service in DSO::mmap_and_copy](https://junglewise.ai/threats/cve-2026-38641-redox-os-relibc-denial-of-service-in-dso-mmap-and-copy)
- [Redox OS relibc Denial of Service in strptime via multibyte characters](https://junglewise.ai/threats/cve-2026-38639-redox-os-relibc-denial-of-service-in-strptime-via-multibyte)
- [Redox OS relibc Denial of Service in __assert_fail](https://junglewise.ai/threats/cve-2026-38640-redox-os-relibc-denial-of-service-in-assert-fail)
- [Redox OS relibc Denial of Service in pthread_rwlockattr_setpshared](https://junglewise.ai/threats/cve-2026-38637-redox-os-relibc-denial-of-service-in-pthread-rwlockattr)