| Title | cesanta mJS v1.26 Heap-based Buffer Overflow |
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| Description | A heap buffer overflow vulnerability exists in the lexical parsing module of the mjs JavaScript engine.
The vulnerability is located in the `skip_spaces_and_comments()` function in `src/mjs_tok.c`. When parsing specially crafted input, the function fails to properly validate buffer boundaries, allowing it to read data beyond the allocated heap buffer, resulting in a program crash.
This issue was discovered using libFuzzer with AddressSanitizer. The vulnerability can be reliably triggered with an input containing `0x0A` (single newline character).
Affected versions:
- mJS v1.26
- Commit: cf375c4
Vulnerability Type:
Heap-based Buffer Overflow (CWE-122) |
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| Source | ⚠️ https://github.com/cesanta/mjs/issues/324 |
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| User | lrrh (UID 100159) |
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| Submission | 07/30/2026 13:14 (1 month ago) |
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| Moderation | 09/08/2026 13:09 (1 month later) |
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| Status | Duplicate |
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| VulDB entry | 399773 [Cesanta mJS up to 1.26 src/mjs_tok.c skip_spaces_and_comments heap-based overflow] |
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| Points | 0 |
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