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Detect UTF-16 surrogates in isc_utf8_valid()

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UTF-8 standard forbid usage of unicode character between the range of
0xD800..0xDFFF (reserved, and used as UTF-16 surrogates, see RFC 3629).

However, `usc_utf8_valid()` was not checking if the encoded unicode
character was in this range, which then would accept invalid UTF-8
strings. This is now fixed.
This commit is contained in:
Colin Vidal 2026-07-02 09:52:09 +02:00
parent 094efe68e3
commit ad5e8fee8d
1 changed files with 38 additions and 0 deletions
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38
lib/isc/utf8.c
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@ -33,9 +33,20 @@ isc_utf8_valid(const unsigned char *buf, size_t len) {
REQUIRE(buf != NULL);
for (size_t i = 0; i < len; i++) {
/*
* ASCII character range (first row).
*/
if (buf[i] <= 0x7f) {
continue;
}
/*
* 0x80 -> 1000 0000
* 0xC0 -> 1100 0000
* 0xE0 -> 1110 0000
*
* Is unicode character is encoded using 2 bytes (second row).
*/
if ((i + 1) < len && (buf[i] & 0xe0) == 0xc0 &&
(buf[i + 1] & 0xc0) == 0x80)
{
@ -47,6 +58,15 @@ isc_utf8_valid(const unsigned char *buf, size_t len) {
}
continue;
}
/*
* 0x80 -> 1000 0000
* 0xC0 -> 1100 0000
* 0xE0 -> 1110 0000
* 0xF0 -> 1111 0000
*
* Is unicode character is encoded within 3 bytes (third row).
*/
if ((i + 2) < len && (buf[i] & 0xf0) == 0xe0 &&
(buf[i + 1] & 0xc0) == 0x80 && (buf[i + 2] & 0xc0) == 0x80)
{
@ -57,8 +77,26 @@ isc_utf8_valid(const unsigned char *buf, size_t len) {
if (w < 0x0800) {
return false;
}
/*
* Unicode range 0xD800..0xDFFF is reserved (UTF16
* surrogates)
*/
if (w >= 0xD800 && w <= 0xDFFF) {
return false;
}
continue;
}
/*
* 0x80 -> 1000 0000
* 0xC0 -> 1100 0000
* 0xE0 -> 1110 0000
* 0xF0 -> 1111 0000
* 0xF8 -> 1111 1000
*
* Is unicode character is encoded within 4 bytes (fourth row).
*/
if ((i + 3) < len && (buf[i] & 0xf8) == 0xf0 &&
(buf[i + 1] & 0xc0) == 0x80 &&
(buf[i + 2] & 0xc0) == 0x80 && (buf[i + 3] & 0xc0) == 0x80)