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Abhishek Bachiphale
b4c4853624
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>
35 lines
1.3 KiB
Diff
35 lines
1.3 KiB
Diff
commit 434d68f2eb1a58744470698483a3ae09b5a9a870
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Author: Simon Kelley <simon@thekelleys.org.uk>
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Date: Wed Mar 25 23:22:37 2026 +0000
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Fix broken client subnet validation. CVE-2026-4893
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Bug report from Royce M <royce@xchglabs.com>
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Location: forward.c:713, edns0.c:421
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With --add-subnet enabled, process_reply() passes the OPT record
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length (~23 bytes) instead of the packet length to check_source().
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All internal bounds checks fail, and the function always returns 1.
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ECS source validation per RFC 7871 Section 9.2 is completely bypassed.
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CVE: CVE-2026-4893
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Upstream-Status: Backport [ https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=e3a26d092e47bf1d18aeadb758e4ca35c83b5f2d ]
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Signed-off-by: Abhishek Bachiphale <Abhishek.Bachiphale@windriver.com>
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diff --git a/src/forward.c b/src/forward.c
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index e2f64c0..208480d 100644
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--- a/src/forward.c
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+++ b/src/forward.c
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@@ -724,7 +724,7 @@ static size_t process_reply(struct dns_header *header, time_t now, struct server
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/* Get extended RCODE. */
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rcode |= sizep[2] << 4;
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- if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, plen, pheader, query_source))
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+ if (option_bool(OPT_CLIENT_SUBNET) && !check_source(header, n, pheader, query_source))
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{
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my_syslog(LOG_WARNING, _("discarding DNS reply: subnet option mismatch"));
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return 0;
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