# CVE-2026-38636: relibc seekdir() denial of service via invalid offset

Source: https://junglewise.ai/threats/cve-2026-38636-relibc-seekdir-denial-of-service-via-invalid-offset  
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-2026-38636 · Severity: high · CVSS 7.5 · Published 2026-08-28

relibc is a C standard library implementation used in the Redox operating system. The seekdir() function, which repositions a directory stream to a previously saved location, can be crashed by passing a negative offset value that the function does not properly validate, causing the process to panic and become unavailable.

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

## Quick answers

**Is CVE-2026-38636 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-38636 being exploited in the wild.

**How severe is CVE-2026-38636?** 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-2026-38636?** A patch was published on 2026: Fix available in merge request 980 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-38636 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-38636?** 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

The vulnerability is a panic-on-invalid-input flaw in the seekdir() function (src/header/dirent/mod.rs) in relibc. The function calls .expect() on a type conversion operation without first validating that the input offset parameter is non-negative. An attacker can invoke seekdir() with a negative c_long offset value, which causes the .try_into() conversion to fail and trigger the expect() panic, resulting in a denial of service. The attack vector is local; the attacker must be able to execute code that calls the vulnerable function. A fix is available in GitLab merge request 980 (commit 61f42d6b).

## Affected products

- Redox OS relibc commit 61f42d and earlier

## Timeline

- 2026-08-28: disclosed
- 2026: patched: Fix available in merge request 980

## References

- [https://github.com/Marsman1996/pocs/tree/master/redox/CVE-2026-38636](https://github.com/Marsman1996/pocs/tree/master/redox/CVE-2026-38636)
- [https://gitlab.redox-os.org/redox-os/relibc/-/issues/260](https://gitlab.redox-os.org/redox-os/relibc/-/issues/260)

## Related threats

- [relibc index out of bounds in with_argv](https://junglewise.ai/threats/cve-2026-38638-relibc-index-out-of-bounds-in-with-argv)
- [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)