# CVE-2026-3842: QEMU out-of-bounds write in hyperv/syndbg memory mapping

Source: https://junglewise.ai/threats/cve-2026-3842-qemu-out-of-bounds-write-in-hyperv-syndbg-memory-mapping  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-16. Updated: 2026-07-16  
License: CC BY 4.0 with a link back

CVE-2026-3842 · Severity: high · CVSS 7.8 · Published 2026-07-16

QEMU is an open-source virtualization software used to run virtual machines. A security flaw was found that allows a user inside a virtual machine to write data into memory areas they should not be able to access on the host system. This could lead to the virtual machine crashing, unauthorized access to sensitive data, or the corruption of system integrity.

## Quick answers

**Is CVE-2026-3842 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-3842 being exploited in the wild.

**How severe is CVE-2026-3842?** High severity, with a CVSS score of 7.8, published 16 July 2026.

**Which products and versions are affected?** QEMU Project QEMU 7.1.0 to 11.0.0; Red Hat Red Hat Enterprise Linux 10 affected; Red Hat Red Hat Enterprise Linux 6 affected; Red Hat Red Hat Enterprise Linux 7 affected; and 3 more.

**Is there a fix for CVE-2026-3842?** No fixed version is recorded yet. Check the vendor's advisory in the references below. 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-2026-3842 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-3842?** Check whether anything you run is named in the advisory. 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 out-of-bounds (OOB) write vulnerability exists in QEMU, specifically within the hyperv/syndbg component. The issue stems from a missing guard check after calling 'cpu_physical_memory_map()'. If this function returns a length shorter than requested, subsequent write operations using the original length will exceed the allocated buffer. This can result in an OOB write to guest memory or a heap-allocated MMIO bounce buffer. An attacker with local access to a guest VM can exploit this to cause memory corruption, potentially leading to a guest-to-host escape, information disclosure, or denial of service. An upstream fix has been identified in the QEMU GitLab repository.

## Affected products

- QEMU Project QEMU 7.1.0 to 11.0.0
- Red Hat Red Hat Enterprise Linux 10 affected
- Red Hat Red Hat Enterprise Linux 6 affected
- Red Hat Red Hat Enterprise Linux 7 affected
- Red Hat Red Hat Enterprise Linux 8 affected
- Red Hat Red Hat Enterprise Linux 9 affected
- Red Hat Red Hat OpenShift Container Platform 4 affected

## Timeline

- 2026-04-14: disclosed: Initial report in Red Hat Bugzilla
- 2026-07-15: advisory: NVD publication date

## References

- [https://gitlab.com/qemu-project/qemu](https://gitlab.com/qemu-project/qemu)
- [https://access.redhat.com/downloads/content/package-browser/](https://access.redhat.com/downloads/content/package-browser/)
- [https://access.redhat.com/security/cve/CVE-2026-3842](https://access.redhat.com/security/cve/CVE-2026-3842)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2458150](https://bugzilla.redhat.com/show_bug.cgi?id=2458150)