Description
Consider the following snippet within php_url_decode_ex at ext/standard/url.c :
else if (*data == '%' && src_len >= 2 && isxdigit((int) *(data + 1))
&& isxdigit((int) *(data + 2))) {In environments where char is signed by default—as is a common convention— high-bit bytes sign-extend to negative integers when being passed to isxdigit. That violates the ISO C standard's requirement for isxdigit in <ctype.h> to be represenetable as an unsigned char (0 to 255), which leads to UB.
Example (taking \x80 as the byte):
<?php
urldecode("%\x80");
?>Resulted in this output:
(gdb) p *(data+1)
$1 = -128 '\200'
Note that for libraries that implement isxdigit via maps (similar to glibc), if no proper padding is done then OOB read might occur.
PHP Version
Operating System
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Description
Consider the following snippet within
php_url_decode_exatext/standard/url.c:In environments where char is signed by default—as is a common convention— high-bit bytes sign-extend to negative integers when being passed to
isxdigit. That violates the ISO C standard's requirement forisxdigitin<ctype.h>to be represenetable as an unsigned char (0 to 255), which leads to UB.Example (taking
\x80as the byte):Resulted in this output:
Note that for libraries that implement
isxdigitvia maps (similar to glibc), if no proper padding is done then OOB read might occur.PHP Version
Operating System
No response