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fix(c): describe the real hazard in insecure-use-strtok-fn #4022

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fix(c): describe the real hazard in insecure-use-strtok-fn #4022

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fix(c): describe the real hazard in insecure-use-strtok-fn
Eljees Jul 27, 2026
d2e8e14
fix(c): correct state, thread-safety and delimiter wording
Eljees Jul 29, 2026
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9 changes: 6 additions & 3 deletions c/lang/security/insecure-use-strtok-fn.yaml
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Expand Up @@ -2,9 +2,12 @@ rules:
- id: insecure-use-strtok-fn
pattern: strtok(...)
message: >-
Avoid using 'strtok()'. This function directly modifies the first argument buffer,
permanently erasing the
delimiter character. Use 'strtok_r()' instead.
Avoid 'strtok()': it is not reentrant or thread-safe, since it keeps the parser
position in a hidden static buffer, so interleaved or concurrent calls (even on

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 27, 2026

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P2 Badge Describe the saved parser state rather than a buffer

When this diagnostic is shown for any strtok() call, it incorrectly implies that the function stores the parser position in a hidden character buffer. The hidden object is parser state—typically a static pointer into the caller-provided input—while the input itself remains the only token buffer and is modified in place. Since this change is specifically intended to explain the real hazard, calling that state a “static buffer” gives users an inaccurate memory model; describe it as hidden static state or a saved pointer instead.

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unrelated strings) clobber each other's state. It also modifies its input in

@chatgpt-codex-connector chatgpt-codex-connector Bot Jul 27, 2026

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P2 Badge Qualify the thread-safety claim as a portability guarantee

For implementations that keep the tokenizer state in thread-local storage, concurrent calls from different threads do not clobber one another, so the unconditional statement that strtok() is not thread-safe is stronger than the C interface guarantees. The portable problem is that C does not require strtok() to avoid data races, while interleaved calls in the same thread still share state. Phrase this as “not guaranteed to be thread-safe” rather than promising that every implementation exhibits concurrent state corruption.

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place, overwriting each delimiter with a NUL byte. Use the reentrant

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P2 Badge Limit the NUL-overwrite claim to token-ending delimiters

For inputs with leading, trailing, or consecutive delimiters, strtok() skips some delimiters without modifying them and overwrites only the delimiter that terminates each returned token. Thus “overwriting each delimiter” is observably false—for example, tokenizing ",,a,,b,," leaves several commas intact—and can mislead users inspecting or reusing the mutated buffer. State that token-ending delimiters are replaced with NUL bytes instead.

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'strtok_r()' (POSIX) or 'strtok_s()' (C11 Annex K), which keep the scan state in
a caller-provided context.
metadata:
cwe:
- 'CWE-676: Use of Potentially Dangerous Function'
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