# CVE-2026-121743: Ashlar-Vellum Cobalt heap-based buffer overflow in AR file parsing

Source: https://junglewise.ai/threats/cve-2026-121743-ashlar-vellum-cobalt-ar-file-parsing-heap-based-buffer-overflow  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-12. Updated: 2026-11-12  
License: CC BY 4.0 with a link back

CVE-2026-121743 · Severity: high · CVSS 7.8 · Published 2026-11-12

Ashlar-Vellum Cobalt is a design and drafting software used for creating technical drawings. A heap-based buffer overflow in its AR file parser allows an attacker to achieve remote code execution when a user opens a malicious AR file or visits a compromised webpage. An exploit could give an attacker complete control over the user's system to steal data, install malware, or launch further attacks.

Technologies: [Ashlar-Vellum Cobalt](https://junglewise.ai/threats/technologies/ashlar-vellum-cobalt). Vendors: [Ashlar-Vellum](https://junglewise.ai/threats/vendors/ashlar-vellum).

## Quick answers

**Is CVE-2026-121743 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-121743 being exploited in the wild.

**How severe is CVE-2026-121743?** High severity, with a CVSS score of 7.8, published 12 November 2026.

**Which products and versions are affected?** Ashlar-Vellum Cobalt.

**Is there a fix for CVE-2026-121743?** No fixed version is recorded yet. Restrict user interaction with the product until a patch is available; avoid opening AR files from untrusted sources and exercise caution when visiting webpages that may host malicious content. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-121743 attacked?** It is attacked over the network or with local access, in a software library.

**Am I affected by CVE-2026-121743?** Check whether you run Ashlar-Vellum Cobalt. 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.

## How to fix


Restrict user interaction with the product until a patch is available; avoid opening AR files from untrusted sources and exercise caution when visiting webpages that may host malicious content.

## Technical details

The vulnerability is a heap-based buffer overflow caused by insufficient validation of user-supplied data length before copying to a heap buffer during AR file parsing. An attacker can craft a malicious AR file that triggers the overflow to execute arbitrary code in the context of the Cobalt process. User interaction (opening a file or visiting a malicious page) is required; no fix has been released as of the advisory publication date.

## Affected products

- Ashlar-Vellum Cobalt

## Timeline

- 2026-01-22: disclosed: Vulnerability reported to vendor by ZDI
- 2026-01-28: other: Vendor acknowledged receipt
- 2026-07-15: other: Vendor indicated fix was not yet completed
- 2026-11-04: advisory: Coordinated public disclosure and 0-day advisory publication
- 2026-11-12: other: CVE published in NVD

## References

- [https://www.zerodayinitiative.com/advisories/ZDI-26-873/](https://www.zerodayinitiative.com/advisories/ZDI-26-873/)

## Related threats

- [Ashlar-Vellum Cobalt XE file parsing use-after-free remote code execution](https://junglewise.ai/threats/cve-2026-121753-ashlar-vellum-cobalt-xe-file-parsing-use-after-free-remote-code)
- [Ashlar-Vellum Cobalt heap buffer overflow in LI file parsing](https://junglewise.ai/threats/cve-2026-121752-ashlar-vellum-cobalt-li-file-parsing-heap-based-buffer-overflow)
- [Ashlar-Vellum Cobalt stack-based buffer overflow in XE file parsing](https://junglewise.ai/threats/cve-2026-121744-ashlar-vellum-cobalt-xe-file-parsing-stack-based-buffer-overflow)
- [Ashlar-Vellum Cobalt use-after-free in XE file parsing](https://junglewise.ai/threats/cve-2026-121742-ashlar-vellum-cobalt-xe-file-parsing-use-after-free-remote-code)