CVE-2026-61801 moby CVE debrief

Who should care

Defenders of systems using the `github.com/moby/sys/user` package, particularly those using affected versions, should assess exposure and prioritize remediation. This includes operators, platform administrators, vulnerability management teams, and security teams responsible for ensuring system integrity and availability. Immediate action is required to prevent potential denial-of-service attacks.

Why it matters

CVE-2026-61801 is a possible DoS via unbounded parsing of user and group database files in the `github.com/moby/sys/user` package. Defenders should assess exposure, prioritize remediation, and verify inventory.

• Potential denial of service (DoS) due to excessive memory consumption
• Possible termination of affected processes due to out-of-memory conditions
• Need to validate and limit untrusted input before parsing

Technical summary

The `github.com/moby/sys/user` package provides Go utilities for parsing and looking up entries in Unix-style user and group database files. Versions before 0.4.1 do not sufficiently limit entries when parsing `/etc/passwd`- or `/etc/group`-style files, allowing an attacker who can supply a specially crafted file to cause excessive memory consumption and potentially terminate the affected process due to an out-of-memory condition.

Defensive priority

Medium priority for systems using affected versions of the `github.com/moby/sys/user` package

Recommended defensive actions

• Assess exposure of systems using affected versions of the `github.com/moby/sys/user` package
• Prioritize remediation of affected systems
• Verify inventory of systems using the `github.com/moby/sys/user` package
• Apply vendor patch guidance for version 0.4.1 or later
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and source item provide details on the vulnerability and patch. The NVD entry is currently UNCHANGED. Evidence from the CVE Program and NIST NVD confirms the vulnerability in versions before 0.4.1 of the `github.com/moby/sys/user` package. Defenders should verify inventory and assess exposure to ensure systems are updated to version 0.4.1 or later. The vulnerability allows an attacker to cause excessive memory consumption by supplying a specially crafted file.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.