CVE-2025-57849 in Fuse
Summary
by MITRE • 03/13/2026
A container privilege escalation flaw was found in certain Fuse images. This issue stems from the /etc/passwd file being created with group-writable permissions during build time. In certain conditions, an attacker who can execute commands within an affected container, even as a non-root user, can leverage their membership in the root group to modify the /etc/passwd file. This could allow the attacker to add a new user with any arbitrary UID, including UID 0, leading to full root privileges within the container.
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Analysis
by VulDB Data Team • 03/20/2026
This vulnerability represents a critical privilege escalation flaw in Fuse container images that directly violates fundamental security principles of container isolation and access control. The issue manifests through improper file permissions during the container build process, where the /etc/passwd file is created with group-writable permissions. This configuration creates a dangerous attack surface that directly conflicts with the principle of least privilege and demonstrates poor security hygiene in container image construction. The vulnerability is classified under CWE-732 as improper permission assignment for critical resources, which is a well-documented weakness that has been exploited in numerous container security incidents. From an operational perspective, this flaw transforms what should be a restricted user environment into a potential root compromise vector, fundamentally undermining container security boundaries.
The technical exploitation mechanism relies on the attacker's ability to leverage group membership rather than direct root access, making this vulnerability particularly insidious as it can be exploited by users who are not initially privileged. When an attacker executes commands within an affected container, they can modify the group-writable /etc/passwd file to add a new user account with arbitrary UID values, including the critical UID 0 that grants root privileges. This approach bypasses traditional privilege escalation techniques by directly manipulating the user authentication database rather than exploiting kernel vulnerabilities or application flaws. The attack vector demonstrates a classic container escape pattern that aligns with ATT&CK technique T1548.001 for privilege escalation through abuse of group membership and T1068 for local privilege escalation. The exploitation requires minimal prerequisites beyond container execution access and leverages the fundamental assumption that /etc/passwd should not be writable by group members.
The operational impact of this vulnerability extends beyond immediate privilege escalation to encompass broader security implications for containerized environments. Organizations running affected Fuse images face potential complete container compromise, which can serve as a stepping stone for further lateral movement within container orchestration platforms such as kubernetes clusters. This vulnerability directly impacts container security posture by creating persistent backdoors that can survive container restarts, as the modified /etc/passwd file remains in the container image. The flaw also undermines security monitoring capabilities since legitimate root access through user manipulation is indistinguishable from malicious activity. From a compliance perspective, this vulnerability violates security standards such as those outlined in NIST SP 800-190 and ISO 27001, which require proper access controls and privilege management. The vulnerability is particularly concerning in multi-tenant environments where container isolation is expected to prevent cross-contamination between different user workloads.
Mitigation strategies should focus on immediate remediation through container image updates that correct the file permission settings during build time, ensuring that /etc/passwd is created with appropriate restrictive permissions. Organizations must conduct comprehensive inventory assessments to identify all affected Fuse container images across their infrastructure and implement automated scanning solutions to prevent deployment of vulnerable images. The recommended approach includes implementing container image signing and verification processes to ensure only trusted, secure images are deployed. Network segmentation and runtime security controls should be enhanced to detect and prevent unauthorized modifications to critical system files. Additionally, organizations should implement principle of least privilege policies that limit group membership for container users and establish regular security audits of container image configurations. The vulnerability highlights the importance of supply chain security and the need for robust container image security practices that include automated vulnerability scanning, configuration compliance checking, and regular security assessments of container build processes to prevent similar issues in the future.