RACE01 Race Condition (TOCTOU)

What this means

SiteShadow flagged a "time-of-check / time-of-use" pattern where the code checks something (like file existence/permissions) and then uses it later, giving an attacker a window to swap or modify the target.

Why it matters

Attackers can change the file between check and use.

• File overwrite/read: attackers can redirect writes/reads to unintended paths via symlinks or path swaps.
• Privilege escalation: race conditions can bypass authorization checks in edge cases.
• These bugs are hard to reproduce, which often means they survive into production.

Safer examples

1) Use atomic file operations

Open/create with flags that guarantee the check and the use happen together (library/OS dependent).

2) Avoid "check then act" on paths you don't control

Prefer working with file descriptors/handles, not re-resolving paths repeatedly.

3) Use safe temp file patterns

Use platform helpers that create unique files securely rather than manual naming.

How SiteShadow detects it (high level)

• Looks for pairs like exists() → open(), access() → read/write, stat() → use, especially with user-controlled paths.
• Flags risky file patterns commonly associated with TOCTOU.

References

• CWE-362: https://cwe.mitre.org/data/definitions/362.html

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