From 0db06ebc77246d112c19f9b0f48fe9fd9bf15445 Mon Sep 17 00:00:00 2001
From: Abtin Keshavarzian <abtink@google.com>
Date: Wed, 6 May 2026 17:51:17 -0700
Subject: [PATCH] [network-data] reject Context ID 0 in `ContextTlv::IsValid()`
 (#13069)

This commit updates the `ContextTlv::IsValid()` method to reject
Context TLVs that specify a Context ID of zero.

According to the Thread specification, Context ID 0 is reserved for
the Mesh-Local Prefix and should not be distributed in the Network Data.
Adding this check ensures that such invalid TLVs are correctly
identified as malformed and dropped during Network Data processing.
---
 src/core/thread/network_data_tlvs.hpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/core/thread/network_data_tlvs.hpp b/src/core/thread/network_data_tlvs.hpp
index 273c89550..b5ac530c4 100644
--- a/src/core/thread/network_data_tlvs.hpp
+++ b/src/core/thread/network_data_tlvs.hpp
@@ -1128,7 +1128,10 @@ public:
      * @retval TRUE   If the TLV appears to be well-formed.
      * @retval FALSE  If the TLV does not appear to be well-formed.
      */
-    bool IsValid(void) const { return GetLength() >= sizeof(*this) - sizeof(NetworkDataTlv); }
+    bool IsValid(void) const
+    {
+        return (GetLength() >= sizeof(*this) - sizeof(NetworkDataTlv)) && (GetContextId() != 0);
+    }
 
     /**
      * Indicates whether or not the Compress flag is set.