From d5d18ced67e969d6a5052cacdbd7d4b2c97a1a3f Mon Sep 17 00:00:00 2001
From: Evgeny Vereshchagin <evvers@ya.ru>
Date: Wed, 17 Dec 2025 08:11:23 +0000
Subject: [PATCH] core: refuse to create wide-area record browsers when
 wide-area is off

It fixes a bug where it was possible for unprivileged local users to
crash avahi-daemon (with wide-area disabled) by creating record browsers
with the AVAHI_LOOKUP_USE_WIDE_AREA flag set via D-Bus (either by calling
the RecordBrowserNew method directly or by creating hostname/address/service
resolvers/browsers that create those browsers internally themselves).

```
$ gdbus call --system --dest org.freedesktop.Avahi --object-path / --method org.freedesktop.Avahi.Server.ResolveHostName -- -1 -1 yo.local -1 1
Error: GDBus.Error:org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message bus without replying
```
```
dbus-protocol.c: interface=org.freedesktop.Avahi.Server, path=/, member=ResolveHostName
avahi-daemon: wide-area.c:725: avahi_wide_area_scan_cache: Assertion `e' failed.
==307948==
==307948== Process terminating with default action of signal 6 (SIGABRT)
==307948==    at 0x4B3630C: __pthread_kill_implementation (pthread_kill.c:44)
==307948==    by 0x4ADF921: raise (raise.c:26)
==307948==    by 0x4AC74AB: abort (abort.c:77)
==307948==    by 0x4AC741F: __assert_fail_base.cold (assert.c:118)
==307948==    by 0x48D8B85: avahi_wide_area_scan_cache (wide-area.c:725)
==307948==    by 0x48C8953: lookup_scan_cache (browse.c:351)
==307948==    by 0x48C8B1B: lookup_go (browse.c:386)
==307948==    by 0x48C9148: defer_callback (browse.c:516)
==307948==    by 0x48AEA0E: expiration_event (timeeventq.c:94)
==307948==    by 0x489D3AE: timeout_callback (simple-watch.c:447)
==307948==    by 0x489D787: avahi_simple_poll_dispatch (simple-watch.c:563)
==307948==    by 0x489D91E: avahi_simple_poll_iterate (simple-watch.c:605)
==307948==
```

wide-area has been disabled by default since
9c4214146738146e454f098264690e8e884c39bd (v0.9-rc2).

https://github.com/avahi/avahi/security/advisories/GHSA-mhf3-865v-g5rc

CVE: CVE-2025-68276
Upstream-Status: Backport [https://github.com/avahi/avahi/pull/806/commits/0c013e2e819be3bda74cecf48b5f64956cf8a760]

Signed-off-by: Adarsh Jagadish Kamini <adarsh.jagadish.kamini@est.tech>
---
 avahi-core/browse.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/avahi-core/browse.c b/avahi-core/browse.c
index e8a915e..59d53cb 100644
--- a/avahi-core/browse.c
+++ b/avahi-core/browse.c
@@ -541,6 +541,11 @@ AvahiSRecordBrowser *avahi_s_record_browser_prepare(
     AVAHI_CHECK_VALIDITY_RETURN_NULL(server, AVAHI_FLAGS_VALID(flags, AVAHI_LOOKUP_USE_WIDE_AREA|AVAHI_LOOKUP_USE_MULTICAST), AVAHI_ERR_INVALID_FLAGS);
     AVAHI_CHECK_VALIDITY_RETURN_NULL(server, !(flags & AVAHI_LOOKUP_USE_WIDE_AREA) || !(flags & AVAHI_LOOKUP_USE_MULTICAST), AVAHI_ERR_INVALID_FLAGS);
 
+    if ((flags & AVAHI_LOOKUP_USE_WIDE_AREA) && !server->wide_area_lookup_engine) {
+        avahi_server_set_errno(server, AVAHI_ERR_NOT_SUPPORTED);
+        return NULL;
+    }
+
     if (!(b = avahi_new(AvahiSRecordBrowser, 1))) {
         avahi_server_set_errno(server, AVAHI_ERR_NO_MEMORY);
         return NULL;
-- 
2.34.1

