When Agentic Glue Melts: Exploiting Cloudflare Code Mode and Workers

Key Points:

• Five critical vulnerabilities were discovered in Cloudflare's workerd runtime, impacting the Code Mode and Cloudflare Workers, including a cross-tenant secret leak and a sandbox escape.
• The vulnerabilities allow attackers to read memory across tenant boundaries and execute native code on the host, posing significant risks to millions of developers using Cloudflare's platform.
• Immediate updates to workerd version v1.20260619.1 are recommended for self-hosted deployments, while managed Workers have already been patched.

Technical Details: The vulnerabilities include an out-of-bounds read in URLPattern and a use-after-free in zlib, both of which can lead to arbitrary memory access and code execution. These issues exploit the shared memory model of workerd, allowing for cross-tenant attacks.

MITRE ATT&CK Techniques:

• T1078 - Valid Accounts (Defense Evasion)
• T1203 - User Execution (Execution)
• T1204.002 - User Execution: Malicious File (Execution)

IOCs Mentioned: None mentioned.