screen: fix CVE-2025-46804

A minor information leak when running Screen with setuid-root
privileges allosw unprivileged users to deduce information
about a path that would otherwise not be available.

Affected are older Screen versions, as well as version 5.0.0.

Reference:
https://security-tracker.debian.org/tracker/CVE-2025-46804

Upstream-patch:
https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=e0eef5aac453fa98a2664416a56c50ad1d00cb30

(From OE-Core rev: fa14b05383a322f5fe751c81e8c6f1a8a1df8c9e)

Signed-off-by: Divya Chellam <divya.chellam@windriver.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

2 files changed, 132 insertions, 0 deletions

diff --git a/meta/recipes-extended/screen/screen/CVE-2025-46804.patch b/meta/recipes-extended/screen/screen/CVE-2025-46804.patch
new file mode 100644
index 0000000000..4cb1465535
--- /dev/null
+++ b/meta/recipes-extended/screen/screen/CVE-2025-46804.patch
@@ -0,0 +1,131 @@
+From e0eef5aac453fa98a2664416a56c50ad1d00cb30 Mon Sep 17 00:00:00 2001
+From: Matthias Gerstner <matthias.gerstner@suse.de>
+Date: Mon, 12 May 2025 15:26:11 +0200
+Subject: [PATCH] fix CVE-2025-46804: avoid file existence test information
+ leaks
+
+In setuid-root context the current error messages give away whether
+certain paths not accessible by the real user exist and what type they
+have. To prevent this only output generic error messages in setuid-root
+context.
+
+In some situations, when an error is pertaining a directory and the
+directory is owner by the real user then we can still output more
+detailed diagnostics.
+
+This change can lead to less helpful error messages when Screen is
+install setuid-root. More complex changes would be needed to avoid this
+(e.g.  only open the `SocketPath` with raised privileges when
+multi-attach is requested).
+
+There might still be lingering some code paths that allow such
+information leaks, since `SocketPath` is a global variable that is used
+across the code base. The majority of issues should be caught with this
+fix, however.
+
+CVE: CVE-2025-46804
+
+Upstream-Status: Backport [https://cgit.git.savannah.gnu.org/cgit/screen.git/commit/?id=e0eef5aac453fa98a2664416a56c50ad1d00cb30]
+
+Signed-off-by: Divya Chellam <divya.chellam@windriver.com>
+---
+ screen.c | 45 ++++++++++++++++++++++++++++++++++-----------
+ socket.c |  9 +++++++--
+ 2 files changed, 41 insertions(+), 13 deletions(-)
+
+diff --git a/screen.c b/screen.c
+index f2e8171..ef6c26a 100644
+--- a/screen.c
++++ b/screen.c
+@@ -1122,15 +1122,28 @@ int main(int ac, char** av)
+ #endif
+   }
+ 
+-  if (stat(SockPath, &st) == -1)
+-    Panic(errno, "Cannot access %s", SockPath);
+-  else
+-    if (!S_ISDIR(st.st_mode))
++  if (stat(SockPath, &st) == -1) {
++    if (eff_uid == real_uid) {
++      Panic(errno, "Cannot access %s", SockPath);
++    } else {
++      Panic(0, "Error accessing %s", SockPath);
++    }
++  } else if (!S_ISDIR(st.st_mode)) {
++    if (eff_uid == real_uid || st.st_uid == real_uid) {
+       Panic(0, "%s is not a directory.", SockPath);
++    } else {
++      Panic(0, "Error accessing %s", SockPath);
++    }
++  }
+ #ifdef MULTIUSER
+   if (multi) {
+-    if ((int)st.st_uid != multi_uid)
+-      Panic(0, "%s is not the owner of %s.", multi, SockPath);
++    if ((int)st.st_uid != multi_uid) {
++      if (eff_uid == real_uid || st.st_uid == real_uid) {
++        Panic(0, "%s is not the owner of %s.", multi, SockPath);
++      } else {
++        Panic(0, "Error accessing %s", SockPath);
++      }
++    }
+   }
+   else
+ #endif
+@@ -1144,9 +1157,13 @@ int main(int ac, char** av)
+       Panic(0, "You are not the owner of %s.", SockPath);
+ #endif
+   }
+-
+-  if ((st.st_mode & 0777) != 0700)
+-    Panic(0, "Directory %s must have mode 700.", SockPath);
++  if ((st.st_mode & 0777) != 0700) {
++    if (eff_uid == real_uid || st.st_uid == real_uid) {
++      Panic(0, "Directory %s must have mode 700.", SockPath);
++    } else {
++      Panic(0, "Error accessing %s", SockPath);
++    }
++  }
+   if (SockMatch && index(SockMatch, '/'))
+     Panic(0, "Bad session name '%s'", SockMatch);
+   SockName = SockPath + strlen(SockPath) + 1;
+@@ -1184,8 +1201,14 @@ int main(int ac, char** av)
+       else
+         exit(9 + (fo || oth ? 1 : 0) + fo);
+     }
+-    if (fo == 0)
+-      Panic(0, "No Sockets found in %s.\n", SockPath);
++    if (fo == 0) {
++      if (eff_uid == real_uid || st.st_uid == real_uid) {
++        Panic(0, "No Sockets found in %s.\n", SockPath);
++      } else {
++        Panic(0, "Error accessing %s", SockPath);
++      }
++    }
++
+     Msg(0, "%d Socket%s in %s.", fo, fo > 1 ? "s" : "", SockPath);
+     eexit(0);
+   }
+diff --git a/socket.c b/socket.c
+index 3bbd64e..5661e6e 100644
+--- a/socket.c
++++ b/socket.c
+@@ -169,8 +169,13 @@ bool *is_sock;
+   xsetegid(real_gid);
+ #endif
+ 
+-  if ((dirp = opendir(SockPath)) == 0)
+-    Panic(errno, "Cannot opendir %s", SockPath);
++  if ((dirp = opendir(SockPath)) == 0) {
++    if (eff_uid == real_uid) {
++      Panic(errno, "Cannot opendir %s", SockPath);
++    } else {
++      Panic(0, "Error accessing %s", SockPath);
++    }
++  }
+ 
+   slist = 0;
+   slisttail = &slist;
+-- 
+2.40.0
+
diff --git a/meta/recipes-extended/screen/screen_4.9.0.bb b/meta/recipes-extended/screen/screen_4.9.0.bb
index 540a78e04b..574b738dbf 100644
--- a/meta/recipes-extended/screen/screen_4.9.0.bb
+++ b/meta/recipes-extended/screen/screen_4.9.0.bb
@@ -24,6 +24,7 @@ SRC_URI = "${GNU_MIRROR}/screen/screen-${PV}.tar.gz \
            file://CVE-2023-24626.patch \
            file://CVE-2025-46805.patch \
            file://CVE-2025-46802.patch \
+           file://CVE-2025-46804.patch \
           "
 
 SRC_URI[sha256sum] = "f9335281bb4d1538ed078df78a20c2f39d3af9a4e91c57d084271e0289c730f4"