Fix buffer overflow in fscan_pnm_token (pnm2png)#1
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Fix buffer overflow in fscan_pnm_token (pnm2png)#1
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The fscan_pnm_token function in contrib/pngminus/pnm2png.c did not properly check for buffer boundaries while reading numeric tokens from PNM headers. This could lead to a buffer overflow when parsing very long lines, potentially causing denial-of-service behavior. This patch adds a length check to ensure that the token_buf array is not written beyond its allocated size. The buffer is now safely null-terminated and the maximum allowed characters are respected. This affects the pnm2png conversion utility only, and not the core libpng library.
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Summary
This PR fixes a buffer overflow vulnerability in the
fscan_pnm_tokenfunction incontrib/pngminus/pnm2png.c, which is used by thepnm2pngconversion tool.Vulnerability
The original implementation lacked bounds checking when reading tokens from the PNM header. If a header line (e.g., width or height) was excessively long, the function could write past the end of the token buffer, potentially causing a crash or denial of service.
Fix
The patch adds a check to ensure that the buffer is not overrun: