# CVE-2026-57842: NetBSD use-after-free and double-free in COMPAT_NETBSD32 msg_recv_copyin

Source: https://junglewise.ai/threats/cve-2026-57842-netbsd-use-after-free-and-double-free-in-compat-netbsd32-msg-recv  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-11. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-57842 · Severity: high · CVSS 7 · Published 2026-09-11

NetBSD's 32-bit compatibility layer contains a memory safety bug in message receiving code that affects 64-bit systems running 32-bit binaries. A local attacker can exploit this by making a specific system call with particular parameters, causing the kernel to crash or corrupt memory, disrupting system availability and potentially compromising the integrity of running applications.

Technologies: [Netbsd](https://junglewise.ai/threats/technologies/netbsd). Vendors: [Netbsd](https://junglewise.ai/threats/vendors/netbsd).

## Quick answers

**Is CVE-2026-57842 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-57842 being exploited in the wild.

**How severe is CVE-2026-57842?** High severity, with a CVSS score of 7, published 11 September 2026.

**Which products and versions are affected?** Netbsd 8.0 through 8.3, 9.0 through 9.4, 10.0 through 10.1, 11.x (pre-patch).

**Is there a fix for CVE-2026-57842?** A patch was published on 2026-06-27: Fix committed to NetBSD HEAD Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-57842 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-57842?** Check whether you run Netbsd 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 use-after-free and double-free bug in msg_recv_copyin() within the COMPAT_NETBSD32 compatibility layer, caused by a missing return statement on the success code path before the cleanup label. When a 32-bit binary running on a 64-bit NetBSD system calls recvmsg() with msg_iovlen between 9 and IOV_MAX, the kernel allocates an iovec buffer but fails to return after successful processing, instead falling through to error-path cleanup code that frees the buffer. The caller then attempts to free the same buffer, triggering a double-free. An attacker with local code execution privileges can trigger kernel panics or memory corruption. The fix was applied via a simple one-line patch (adding return 0; before the cleanup label) and backported to NetBSD 8, 9, 10, and 11.

## Affected products

- NetBSD NetBSD 8.0 through 8.3, 9.0 through 9.4, 10.0 through 10.1, 11.x (pre-patch)

## Timeline

- 2026-06-26: disclosed: Vulnerability reported to NetBSD via problem report PR #60373
- 2026-06-27: patched: Fix committed to NetBSD HEAD
- 2026-06-29: patched: Backports applied to NetBSD 11, 10, and 9 branches
- 2026-09-11: advisory: CVE-2026-57842 published and indexed in NVD

## References

- [https://gnats.netbsd.org/60373](https://gnats.netbsd.org/60373)
- [https://www.vulncheck.com/advisories/netbsd-compat-netbsd32-double-free-use-after-free-via-recvmsg-msg-iovlen](https://www.vulncheck.com/advisories/netbsd-compat-netbsd32-double-free-use-after-free-via-recvmsg-msg-iovlen)

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