File 0010-Add-recursion-limit-for-ASN.1-indefinite-lengths.patch of Package krb5.30217
From 03bd88eca9d1d0b7e9e1447cd68ebd086163fec0 Mon Sep 17 00:00:00 2001
From: Greg Hudson <ghudson@mit.edu>
Date: Sat, 31 Oct 2020 17:07:05 -0400
Subject: [PATCH] Add recursion limit for ASN.1 indefinite lengths
The libkrb5 ASN.1 decoder supports BER indefinite lengths. It
computes the tag length using recursion; the lack of a recursion limit
allows an attacker to overrun the stack and cause the process to
crash. Reported by Demi Obenour.
CVE-2020-28196:
In MIT krb5 releases 1.11 and later, an unauthenticated attacker can
cause a denial of service for any client or server to which it can
send an ASN.1-encoded Kerberos message of sufficient length.
(cherry picked from commit 57415dda6cf04e73ffc3723be518eddfae599bfd)
ticket: 8959
version_fixed: 1.17.2
(cherry picked from commit 9239fa1d0124bdf3c78c20eb70873e3af2baabb1)
---
src/lib/krb5/asn.1/asn1_encode.c | 16 +++++++++-------
1 file changed, 9 insertions(+), 7 deletions(-)
diff --git a/src/lib/krb5/asn.1/asn1_encode.c b/src/lib/krb5/asn.1/asn1_encode.c
index a7423b642..8c0cda852 100644
--- a/src/lib/krb5/asn.1/asn1_encode.c
+++ b/src/lib/krb5/asn.1/asn1_encode.c
@@ -393,7 +393,7 @@ make_tag(asn1buf *buf, const taginfo *t, size_t len, size_t *retlen)
static asn1_error_code
get_tag(const unsigned char *asn1, size_t len, taginfo *tag_out,
const unsigned char **contents_out, size_t *clen_out,
- const unsigned char **remainder_out, size_t *rlen_out)
+ const unsigned char **remainder_out, size_t *rlen_out, int recursion)
{
asn1_error_code ret;
unsigned char o;
@@ -431,9 +431,11 @@ get_tag(const unsigned char *asn1, size_t len, taginfo *tag_out,
/* Indefinite form (should not be present in DER, but we accept it). */
if (tag_out->construction != CONSTRUCTED)
return ASN1_MISMATCH_INDEF;
+ if (recursion >= 32)
+ return ASN1_OVERFLOW;
p = asn1;
while (!(len >= 2 && p[0] == 0 && p[1] == 0)) {
- ret = get_tag(p, len, &t, &c, &clen, &p, &len);
+ ret = get_tag(p, len, &t, &c, &clen, &p, &len, recursion + 1);
if (ret)
return ret;
}
@@ -652,7 +654,7 @@ split_der(asn1buf *buf, unsigned char *const *der, size_t len,
const unsigned char *contents, *remainder;
size_t clen, rlen;
- ret = get_tag(*der, len, tag_out, &contents, &clen, &remainder, &rlen);
+ ret = get_tag(*der, len, tag_out, &contents, &clen, &remainder, &rlen, 0);
if (ret)
return ret;
if (rlen != 0)
@@ -1259,7 +1261,7 @@ decode_atype(const taginfo *t, const unsigned char *asn1,
const unsigned char *rem;
size_t rlen;
if (!tag->implicit) {
- ret = get_tag(asn1, len, &inner_tag, &asn1, &len, &rem, &rlen);
+ ret = get_tag(asn1, len, &inner_tag, &asn1, &len, &rem, &rlen, 0);
if (ret)
return ret;
/* Note: we don't check rlen (it should be 0). */
@@ -1481,7 +1483,7 @@ decode_sequence(const unsigned char *asn1, size_t len,
for (i = 0; i < seq->n_fields; i++) {
if (len == 0)
break;
- ret = get_tag(asn1, len, &t, &contents, &clen, &asn1, &len);
+ ret = get_tag(asn1, len, &t, &contents, &clen, &asn1, &len, 0);
if (ret)
goto error;
/*
@@ -1539,7 +1541,7 @@ decode_sequence_of(const unsigned char *asn1, size_t len,
*seq_out = NULL;
*count_out = 0;
while (len > 0) {
- ret = get_tag(asn1, len, &t, &contents, &clen, &asn1, &len);
+ ret = get_tag(asn1, len, &t, &contents, &clen, &asn1, &len, 0);
if (ret)
goto error;
if (!check_atype_tag(elemtype, &t)) {
@@ -1625,7 +1627,7 @@ k5_asn1_full_decode(const krb5_data *code, const struct atype_info *a,
*retrep = NULL;
ret = get_tag((unsigned char *)code->data, code->length, &t, &contents,
- &clen, &remainder, &rlen);
+ &clen, &remainder, &rlen, 0);
if (ret)
return ret;
/* rlen should be 0, but we don't check it (and due to padding in
--
2.29.2