Gitweb:
https://git.exim.org/exim.git/commitdiff/654056e44fc93a0ee7c09d1228933e8af6862206
Commit: 654056e44fc93a0ee7c09d1228933e8af6862206
Parent: a355463cfc6479893c6212056a5ca7e6bf2d450b
Author: Jeremy Harris <jgh146exb@???>
AuthorDate: Tue Oct 10 12:45:27 2023 +0100
Committer: Heiko Schlittermann (HS12-RIPE) <hs@???>
CommitDate: Sat Oct 14 23:50:37 2023 +0200
SPF: harden against crafted DNS responses
(cherry picked from commit 4f07f38374f8662c318699fb30432273ffcfe0d3)
---
src/src/spf.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/src/src/spf.c b/src/src/spf.c
index db6eea3a8..1981d81b6 100644
--- a/src/src/spf.c
+++ b/src/src/spf.c
@@ -120,6 +120,7 @@ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
switch(rr_type)
{
case T_MX:
+ if (rr->size < 2) continue;
s += 2; /* skip the MX precedence field */
case T_PTR:
{
@@ -135,6 +136,7 @@ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
gstring * g = NULL;
uschar chunk_len;
+ if (rr->size < 1+6) continue; /* min for version str */
if (strncmpic(rr->data+1, US SPF_VER_STR, 6) != 0)
{
HDEBUG(D_host_lookup) debug_printf("not an spf record: %.*s\n",
@@ -142,9 +144,12 @@ for (dns_record * rr = dns_next_rr(dnsa, &dnss, RESET_ANSWERS); rr;
continue;
}
- for (int off = 0; off < rr->size; off += chunk_len)
+ /* require 1 byte for the chunk_len */
+ for (int off = 0; off < rr->size - 1; off += chunk_len)
{
- if (!(chunk_len = s[off++])) break;
+ if ( !(chunk_len = s[off++])
+ || rr->size < off + chunk_len /* ignore bogus size chunks */
+ ) break;
g = string_catn(g, s+off, chunk_len);
}
if (!g)
--
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