CVE-2020-13845 in Singularity
Summary
by MITRE • 01/25/2023
Sylabs Singularity 3.0 through 3.5 has Improper Validation of an Integrity Check Value. Image integrity is not validated when an ECL policy is enforced. The fingerprint required by the ECL is compared against the signature object descriptor(s) in the SIF file, rather than to a cryptographically validated signature.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability identified as CVE-2020-13845 affects Sylabs Singularity versions 3.0 through 3.5 and represents a critical flaw in the container image validation mechanism. This issue stems from improper validation of integrity check values within the Enhanced Container Lockdown (ECL) policy enforcement system. The vulnerability specifically impacts how Singularity handles cryptographic signature verification when processing SIF (Singularity Image Format) files, creating a significant security gap that undermines the integrity protection mechanisms designed to prevent unauthorized modifications to container images.
The technical flaw manifests in the validation process where the system compares the expected fingerprint against signature object descriptors within the SIF file rather than performing proper cryptographic validation of the actual signature. This approach bypasses essential cryptographic checks that should verify the authenticity and integrity of container images. The vulnerability falls under CWE-347, which addresses improper validation of cryptographic signatures, and represents a failure in implementing proper cryptographic verification procedures. When ECL policies are enforced, the system should validate that the signature matches the expected cryptographic fingerprint through proper signature verification algorithms, but instead performs only a superficial comparison against descriptor metadata.
The operational impact of this vulnerability is severe as it allows attackers to potentially bypass container security controls by manipulating the signature object descriptors while maintaining the appearance of a valid signature. An attacker could modify container images and substitute their own content without detection, as the integrity check would pass due to the flawed validation mechanism. This creates a false sense of security for users who rely on Singularity's ECL policies to enforce image integrity. The vulnerability particularly affects environments where container security is paramount, such as high-security research institutions, financial services, and government agencies that depend on containerized applications. Attackers could exploit this weakness to inject malicious code into container images, potentially compromising entire computational environments that rely on Singularity for container orchestration.
Mitigation strategies should focus on immediate remediation through upgrading to Singularity versions 3.5.1 or later where the vulnerability has been addressed. Organizations should also implement additional verification mechanisms such as manual signature validation using external tools, regular integrity audits of container images, and implementation of multi-layered security controls that do not rely solely on the affected ECL policy. The fix addresses the core issue by implementing proper cryptographic signature validation instead of descriptor comparison, aligning with ATT&CK technique T1553.004 for Validated Signatures and ensuring proper cryptographic integrity checks are performed. Security teams should also consider implementing container image scanning tools that can detect such anomalies and establish monitoring procedures to identify potential exploitation attempts. Organizations using older versions of Singularity should immediately disable ECL policy enforcement until a secure upgrade is completed, as the vulnerability creates a direct path for privilege escalation and code injection attacks against containerized environments.