An OpenCode vulnerability allowed malicious or hijacked MCP servers to execute code on Windows or WSL during developer sign-in due to improper escaping in browser helper calls.
Anomaly fixed the flaw in version 1.18.33.
OpenCode connects to external services to add new tools. On Windows and WSL, during the connection process, the program would send an email address to a helper system to open it in the web crawler. Because this address did not pass the necessary checks, a carefully crafted address could instruct the computer to run programs in secret.
Who is affected and how was it fixed?
The issue affects OpenCode versions 1.0.137 through 1.18.32. macOS and Linux computers are not affected, as the program opens the launcher differently on these systems.
Anomaly released version 1.18.33 on September 28, 2026, which fixes the issue. Anomaly did not request an official ID number or issue a security warning, claiming that external servers were outside its trust boundaries.
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Researchers at Pillar Security discovered the issue, privately disclosed it to Anomaly on August 29, 2026, and publicly disclosed it on October 19, 2026, rating it 9.8 out of 10.
What users should do
Those using OpenCode on Windows or WSL should immediately upgrade to version 1.18.33 or later.
Alternatively, users can check which services they have connected by typing opencode mcp list and remove any servers they don't know or trust.
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