# CVE-2026-38639: Redox OS relibc Denial of Service in strptime via multibyte characters

Source: https://junglewise.ai/threats/cve-2026-38639-redox-os-relibc-denial-of-service-in-strptime-via-multibyte  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-26. Updated: 2026-06-26  
License: CC BY 4.0 with a link back

CVE-2026-38639 · Severity: info · Published 2026-06-26

relibc is a standard C library used by the Redox operating system to handle core system functions like time and date processing. A flaw in how the library handles specific text characters can cause a program to crash unexpectedly when processing specially formatted dates. This could allow a local user to disrupt services or cause applications to stop working, leading to a 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-2026-38639 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-38639 being exploited in the wild.

**How severe is CVE-2026-38639?** Informational severity, published 26 June 2026.

**Which products and versions are affected?** Redox OS Relibc commit ab6a2e73223c9ff30cbbf5069d6758afb4cf08e3.

**Is there a fix for CVE-2026-38639?** A patch was published on 2026-02-10: Merge request 990 submitted to fix the issue. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-38639 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-38639?** 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

A vulnerability exists in relibc's implementation of strptime.rs (specifically within parse_month and parse_weekday) due to improper handling of UTF-8 character boundaries during string slicing. When the library attempts to slice a string based on the length of expected month or weekday names, it may attempt to slice in the middle of a multibyte character, triggering a Rust runtime panic. An attacker can exploit this by passing a crafted multibyte string to the strptime() function, leading to an immediate application crash (Denial of Service). The issue was identified in commit ab6a2e7 and addressed in merge request 990.

## Affected products

- Redox OS relibc commit ab6a2e73223c9ff30cbbf5069d6758afb4cf08e3

## Timeline

- 2026-02-10: patched: Merge request 990 submitted to fix the issue.
- 2026-06-26: advisory: CVE-2026-38639 published.

## References

- [https://github.com/Marsman1996/pocs/tree/master/redox/CVE-2026-38639](https://github.com/Marsman1996/pocs/tree/master/redox/CVE-2026-38639)
- [https://gitlab.redox-os.org/redox-os/relibc/-/issues/265](https://gitlab.redox-os.org/redox-os/relibc/-/issues/265)
- [https://gitlab.redox-os.org/redox-os/relibc/-/merge_requests/990](https://gitlab.redox-os.org/redox-os/relibc/-/merge_requests/990)
- [https://gitlab.redox-os.org/redox-os/relibc/-/work_items/265](https://gitlab.redox-os.org/redox-os/relibc/-/work_items/265)

## 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)
- [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 __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)