# CVE-2026-61801: moby/sys/user denial of service via unbounded parsing

Source: https://junglewise.ai/threats/cve-2026-61801-github-com-moby-sys-user-has-a-possible-dos-via-unbounded-parsing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-08. Updated: 2026-10-08  
License: CC BY 4.0 with a link back

CVE-2026-61801 · Severity: medium · CVSS 5.5 · Published 2026-10-08

A Go library used by container runtimes to parse user and group database files can be forced to consume excessive memory when processing specially crafted files. An attacker who can supply a malicious passwd or group file could cause the application to run out of memory and crash, disrupting service availability.

Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Moby](https://junglewise.ai/threats/vendors/moby).

## Quick answers

**Is CVE-2026-61801 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-61801 being exploited in the wild.

**How severe is CVE-2026-61801?** Medium severity, with a CVSS score of 5.5, published 8 October 2026.

**Which products and versions are affected?** github.com/moby/sys/user (Go) <= 0.4.0, SEMVER:introduced=0,fixed=0.4.1; Moby Sys/User before v0.4.1.

**Is there a fix for CVE-2026-61801?** Yes. github.com/moby/sys/user (Go): upgrade to 0.4.1 or later. Until then: Avoid parsing user-supplied or untrusted passwd or group files with affected versions. If processing untrusted input is necessary, validate and limit accepted entries before parsing with moby/sys/user. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-61801 attacked?** It is attacked with local access.

**Am I affected by CVE-2026-61801?** Check whether you run github.com/moby/sys/user (Go) or Moby Sys/User 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.

## How to fix

- github.com/moby/sys/user (Go): upgrade to 0.4.1 or later

  ```sh
  go get github.com/moby/sys/user@v0.4.1
  ```


Avoid parsing user-supplied or untrusted passwd or group files with affected versions. If processing untrusted input is necessary, validate and limit accepted entries before parsing with moby/sys/user.

## Technical details

The moby/sys/user library fails to enforce limits on entries when parsing /etc/passwd or /etc/group-style files, allowing a specially crafted file to trigger unbounded memory allocation and exhaustion. The vulnerability requires an attacker to be able to control or supply the contents of the parsed file. A fix enforcing proper bounds checking was introduced in v0.4.1.

## Affected products

- moby sys/user before v0.4.1

## Identifiers

- CVE-2026-61801
- GHSA-mjcv-p78q-w5fw
- GO-2026-6686

## Timeline

- 2026-10-08: disclosed