CVE-2017-0903

What it actually does

YAML deserialization of gem specifications bypasses class whitelists, allowing specially crafted serialized objects to escalate to remote code execution.

Why it matters to the business

Attackers could gain full control of affected systems, leading to data theft, service disruption, or further network compromise; the flaw has been public for years with stable exploit likelihood, so unpatched instances remain a persistent risk in dependent ecosystems.

How an attack unfolds

An attacker crafts a malicious gem specification containing a serialized object that evades the YAML whitelist, causing the vulnerable RubyGems parser to execute arbitrary code upon deserialization during gem operations.

How to fix it

Upgrade all affected packages to the fixed versions provided: prometheus (Chainguard) to 2.51.0-r1 or later and prometheus (Wolfi) to 2.51.0-r1 or later; replace any bundled RubyGems instances older than 2.6.14.

How to confirm the fix worked

Verify installed package versions against the listed fixed releases, scan for outdated RubyGems components in build and runtime environments, and confirm absence of vulnerable gem specification parsing code paths.

Typical attack path

1. Identify a target system using an affected RubyGems version between 2.0.0 and 2.6.13.
2. Deliver a specially crafted gem specification containing a bypass serialized object via network-accessible gem handling.
3. Trigger deserialization during gem installation, update, or specification processing.
4. Achieve remote code execution to establish persistence or escalate privileges.

How to detect it

Review historical logs from gem processing services for unusual deserialization events or unexpected code execution during package operations; search archived network traffic for gem specification payloads around the time of any suspected compromise.

What your security team should do

• Immediately upgrade all instances to the specified fixed versions to eliminate exposure.
• Audit dependency trees for any remaining RubyGems 2.0.0-2.6.13 usage across the ecosystem.
• Implement runtime controls or network segmentation around gem handling services until upgrades complete.
• Monitor EPSS and KEV updates for any future changes in exploit activity.