From e0d05145e1e36ff4fdf7615f762f58f8000f44e7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ond=C5=99ej=20Sur=C3=BD?= <ondrej@isc.org>
Date: Sat, 14 Feb 2026 14:43:41 +0100
Subject: [PATCH] Invalid NSEC3 can cause OOB read of the isdelegation() stack

When .next_length is longer than NSEC3_MAX_HASH_LENGTH, it causes a
harmless out-of-bound read of the isdelegation() stack.  This patch
fixes the issue by skipping NSEC3 records with an oversized hash length
during validation.

(cherry picked from commit 67b4fb56e40bf856e1fccd41e752d5f486b5b569)
---
 lib/dns/rdata/generic/nsec3_50.c | 1 +
 lib/dns/validator.c              | 3 +++
 2 files changed, 4 insertions(+)

diff --git a/lib/dns/rdata/generic/nsec3_50.c b/lib/dns/rdata/generic/nsec3_50.c
index 600a90f9bd..9f4d4e5a99 100644
--- a/lib/dns/rdata/generic/nsec3_50.c
+++ b/lib/dns/rdata/generic/nsec3_50.c
@@ -313,6 +313,7 @@ tostruct_nsec3(ARGS_TOSTRUCT) {
 	nsec3->len = region.length;
 	nsec3->typebits = mem_maybedup(mctx, region.base, region.length);
 	nsec3->mctx = mctx;
+
 	return ISC_R_SUCCESS;
 }
 
diff --git a/lib/dns/validator.c b/lib/dns/validator.c
index 0cd2cfb6c2..4ab4ee407e 100644
--- a/lib/dns/validator.c
+++ b/lib/dns/validator.c
@@ -340,6 +340,9 @@ trynsec3:
 			if (nsec3.hash != 1) {
 				continue;
 			}
+			if (nsec3.next_length > NSEC3_MAX_HASH_LENGTH) {
+				continue;
+			}
 			length = isc_iterated_hash(
 				hash, nsec3.hash, nsec3.iterations, nsec3.salt,
 				nsec3.salt_length, name->ndata, name->length);