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From: bradh352 <brad@brad-house.com>
Date: Fri, 11 Jun 2021 11:27:45 -0400
Subject: [1/2] ares_expand_name() should escape more characters
Origin: https://github.com/c-ares/c-ares/commit/362f91d807d293791008cdb7616d40f7784ece83
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2021-3672
RFC1035 5.1 specifies some reserved characters and escaping sequences
that are allowed to be specified. Expand the list of reserved characters
and also escape non-printable characters using the \DDD format as
specified in the RFC.
Bug Reported By: philipp.jeitner@sit.fraunhofer.de
Fix By: Brad House (@bradh352)
CVE: CVE-2021-3672
Upstream-Status: Backport [http://snapshot.debian.org/archive/debian-security/20210810T064453Z/pool/updates/main/c/c-ares/c-ares_1.17.1-1%2Bdeb11u1.debian.tar.xz]
Signed-off-by: Neetika Singh <Neetika.Singh@kpit.com>
---
ares_expand_name.c | 41 +++++++++++++++++++++++++++++++++++---
1 file changed, 38 insertions(+), 3 deletions(-)
diff --git a/ares_expand_name.c b/ares_expand_name.c
index 407200ef5b4b..f1c874a97cfc 100644
--- a/ares_expand_name.c
+++ b/ares_expand_name.c
@@ -32,6 +32,26 @@
static int name_length(const unsigned char *encoded, const unsigned char *abuf,
int alen);
+/* Reserved characters for names that need to be escaped */
+static int is_reservedch(int ch)
+{
+ switch (ch) {
+ case '"':
+ case '.':
+ case ';':
+ case '\\':
+ case '(':
+ case ')':
+ case '@':
+ case '$':
+ return 1;
+ default:
+ break;
+ }
+
+ return 0;
+}
+
/* Expand an RFC1035-encoded domain name given by encoded. The
* containing message is given by abuf and alen. The result given by
* *s, which is set to a NUL-terminated allocated buffer. *enclen is
@@ -111,9 +131,18 @@ int ares_expand_name(const unsigned char *encoded, const unsigned char *abuf,
p++;
while (len--)
{
- if (*p == '.' || *p == '\\')
+ if (!isprint(*p)) {
+ /* Output as \DDD for consistency with RFC1035 5.1 */
+ *q++ = '\\';
+ *q++ = '0' + *p / 100;
+ *q++ = '0' + (*p % 100) / 10;
+ *q++ = '0' + (*p % 10);
+ } else if (is_reservedch(*p)) {
*q++ = '\\';
- *q++ = *p;
+ *q++ = *p;
+ } else {
+ *q++ = *p;
+ }
p++;
}
*q++ = '.';
@@ -171,7 +200,13 @@ static int name_length(const unsigned char *encoded, const unsigned char *abuf,
encoded++;
while (offset--)
{
- n += (*encoded == '.' || *encoded == '\\') ? 2 : 1;
+ if (!isprint(*encoded)) {
+ n += 4;
+ } else if (is_reservedch(*encoded)) {
+ n += 2;
+ } else {
+ n += 1;
+ }
encoded++;
}
n++;
--
2.32.0
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