From b4c48536242d9aa7d1eaf968152fc83edea41923 Mon Sep 17 00:00:00 2001 From: Abhishek Bachiphale Date: Mon, 18 May 2026 22:43:35 +0530 Subject: [PATCH] dnsmasq: fix CVE-2026-4893 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 Signed-off-by: Khem Raj --- .../recipes-support/dnsmasq/dnsmasq_2.92.bb | 1 + .../dnsmasq/files/CVE-2026-4893.patch | 34 +++++++++++++++++++ 2 files changed, 35 insertions(+) create mode 100644 meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch diff --git a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb index cf900328ed..4ae650f7e7 100644 --- a/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb +++ b/meta-networking/recipes-support/dnsmasq/dnsmasq_2.92.bb @@ -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" diff --git a/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch new file mode 100644 index 0000000000..af7e4119e1 --- /dev/null +++ b/meta-networking/recipes-support/dnsmasq/files/CVE-2026-4893.patch @@ -0,0 +1,34 @@ +commit 434d68f2eb1a58744470698483a3ae09b5a9a870 +Author: Simon Kelley +Date: Wed Mar 25 23:22:37 2026 +0000 + +Fix broken client subnet validation. CVE-2026-4893 + +Bug report from Royce M + +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 + +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;