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dnsmasq: fix CVE-2026-4893

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An information disclosure vulnerability in dnsmasq allows remote
attackers to bypass source checks via a crafted DNS packet with
RFC 7871 client subnet information.

Reference:
[ https://nvd.nist.gov/vuln/detail/CVE-2026-4893 ]

Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
Signed-off-by: Khem Raj <khem.raj@oss.qualcomm.com>
This commit is contained in:
Abhishek Bachiphale
2026-05-18 22:43:35 +05:30
committed by Khem Raj
parent 21c3d7eb6f
commit b4c4853624
2 changed files with 35 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files
meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb
+1
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@@ -19,6 +19,7 @@ SRC_URI = "http://www.thekelleys.org.uk/dnsmasq/${@['archive/', ''][float(d.getV
file://CVE-2026-4890.patch \
file://CVE-2026-4891.patch \
file://CVE-2026-4892.patch \
file://CVE-2026-4893.patch \
"
SRC_URI[sha256sum] = "fd908e79ff37f73234afcb6d3363f78353e768703d92abd8e3220ade6819b1e1"
meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch
+34
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@@ -0,0 +1,34 @@
commit 434d68f2eb1a58744470698483a3ae09b5a9a870
Author: Simon Kelley <simon@thekelleys.org.uk>
Date: Wed Mar 25 23:22:37 2026 +0000
Fix broken client subnet validation. CVE-2026-4893
Bug report from Royce M <royce@xchglabs.com>
Location: forward.c:713, edns0.c:421
With --add-subnet enabled, process_reply() passes the OPT record
length (~23 bytes) instead of the packet length to check_source().
All internal bounds checks fail, and the function always returns 1.
ECS source validation per RFC 7871 Section 9.2 is completely bypassed.
CVE: CVE-2026-4893
Upstream-Status: Backport [ https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=e3a26d092e47bf1d18aeadb758e4ca35c83b5f2d ]
Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
diff --git a/src/forward.c b/src/forward.c
index e2f64c0..208480d 100644
--- a/src/forward.c
+++ b/src/forward.c
@@ -724,7 +724,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
/* Get extended RCODE. */
rcode |= sizep[2] << 4;
- if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, plen, pheader, query_source))
+ if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, n, pheader, query_source))
{
my_syslog(LOG_WARNING, _("discarding DNS reply: subnet option mismatch"));
return 0;