diff -pruN 5.15.17+dfsg-1/debian/changelog 5.15.17+dfsg-1ubuntu1/debian/changelog
--- 5.15.17+dfsg-1/debian/changelog	2025-05-24 19:32:13.000000000 +0000
+++ 5.15.17+dfsg-1ubuntu1/debian/changelog	2025-07-11 13:12:23.000000000 +0000
@@ -1,3 +1,11 @@
+qtbase-opensource-src (5.15.17+dfsg-1ubuntu1) questing; urgency=medium
+
+  * Merge with Debian experimental, remaining changes:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+    - Disable _Z5qHashgj symbol on ppc64el.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Fri, 11 Jul 2025 16:12:23 +0300
+
 qtbase-opensource-src (5.15.17+dfsg-1) experimental; urgency=medium
 
   * New upstream release.
@@ -33,6 +41,21 @@ qtbase-opensource-src (5.15.16+dfsg-1) e
 
  -- Dmitry Shachnev <mitya57@debian.org>  Fri, 24 Jan 2025 22:26:02 +0300
 
+qtbase-opensource-src (5.15.15+dfsg-6) unstable; urgency=medium
+
+  * Backport upstream patch to fix assertion errors in data: URL parsing
+    (CVE-2025-5455, closes: #1108475).
+
+ -- Dmitry Shachnev <mitya57@debian.org>  Sun, 29 Jun 2025 22:50:45 +0300
+
+qtbase-opensource-src (5.15.15+dfsg-5ubuntu1) questing; urgency=medium
+
+  * Merge with Debian. Remaining changes:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+    - Update symbols on ppc64el.
+
+ -- Rik Mills <rikmills@kde.org>  Sat, 10 May 2025 14:10:51 +0100
+
 qtbase-opensource-src (5.15.15+dfsg-5) unstable; urgency=medium
 
   * Backport upstream patch to add null checks in table iface methods in
@@ -41,6 +64,14 @@ qtbase-opensource-src (5.15.15+dfsg-5) u
 
  -- Dmitry Shachnev <mitya57@debian.org>  Mon, 24 Mar 2025 15:42:48 +0300
 
+qtbase-opensource-src (5.15.15+dfsg-4ubuntu1) plucky; urgency=medium
+
+  * Merge with Debian. Remaining changes:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+  * Merge fixes (LP: #2098556) 
+
+ -- Rik Mills <rikmills@kde.org>  Sat, 15 Feb 2025 14:00:03 +0000
+
 qtbase-opensource-src (5.15.15+dfsg-4) unstable; urgency=medium
 
   * Fix containsTLDEntry() crash when tldChunkCount >= 3 (closes: #1095423).
@@ -63,6 +94,19 @@ qtbase-opensource-src (5.15.15+dfsg-3) u
 
  -- Pino Toscano <pino@debian.org>  Fri, 07 Feb 2025 07:20:36 +0100
 
+qtbase-opensource-src (5.15.15+dfsg-1ubuntu2) plucky; urgency=medium
+
+  * No-change rebuild for icu soname change.
+
+ -- Matthias Klose <doko@ubuntu.com>  Tue, 07 Jan 2025 08:36:52 +0100
+
+qtbase-opensource-src (5.15.15+dfsg-1ubuntu1) oracular; urgency=medium
+
+  * Merge with Debian experimental, remaining change:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Mon, 09 Sep 2024 19:15:29 +0300
+
 qtbase-opensource-src (5.15.15+dfsg-2) unstable; urgency=medium
 
   * Upload to unstable.
@@ -99,6 +143,13 @@ qtbase-opensource-src (5.15.14+dfsg-1) e
 
  -- Dmitry Shachnev <mitya57@debian.org>  Sun, 26 May 2024 17:32:51 +0300
 
+qtbase-opensource-src (5.15.13+dfsg-4ubuntu1) oracular; urgency=medium
+
+  * Merge with Debian unstable, remaining change:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Fri, 26 Jul 2024 14:47:52 +0300
+
 qtbase-opensource-src (5.15.13+dfsg-4) unstable; urgency=medium
 
   * Backport upstream patch to fix qfutureinterface.h for GCC 14
@@ -126,6 +177,13 @@ qtbase-opensource-src (5.15.13+dfsg-2) u
 
  -- Dmitry Shachnev <mitya57@debian.org>  Tue, 21 May 2024 10:53:43 +0300
 
+qtbase-opensource-src (5.15.13+dfsg-1ubuntu1) noble; urgency=medium
+
+  * Merge with Debian experimental, remaining change:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Thu, 28 Mar 2024 11:19:11 +0300
+
 qtbase-opensource-src (5.15.13+dfsg-1) experimental; urgency=medium
 
   * Merge 5.15.10+dfsg-7.2 upload from unstable.
@@ -143,6 +201,43 @@ qtbase-opensource-src (5.15.13+dfsg-1) e
 
  -- Dmitry Shachnev <mitya57@debian.org>  Sat, 09 Mar 2024 14:24:14 +0300
 
+qtbase-opensource-src (5.15.12+dfsg-3ubuntu6) noble; urgency=medium
+
+  * No-change rebuild against libcups2t64
+
+ -- Michael Hudson-Doyle <michael.hudson@ubuntu.com>  Wed, 20 Mar 2024 13:56:07 +1300
+
+qtbase-opensource-src (5.15.12+dfsg-3ubuntu5) noble; urgency=medium
+
+  * Merge 5.15.10+dfsg-7.2 upload from Debian unstable.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Fri, 15 Mar 2024 01:00:58 +0300
+
+qtbase-opensource-src (5.15.12+dfsg-3ubuntu4) noble; urgency=medium
+
+  * No-change rebuild against libglib2.0-0t64
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Mon, 11 Mar 2024 23:33:19 +0000
+
+qtbase-opensource-src (5.15.12+dfsg-3ubuntu3) noble; urgency=medium
+
+  * No-change rebuild against libssl3t64
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Mon, 04 Mar 2024 21:09:22 +0000
+
+qtbase-opensource-src (5.15.12+dfsg-3ubuntu2) noble; urgency=medium
+
+  * No-change rebuild against libpng16-16t64
+
+ -- Steve Langasek <steve.langasek@ubuntu.com>  Thu, 29 Feb 2024 08:02:22 +0000
+
+qtbase-opensource-src (5.15.12+dfsg-3ubuntu1) noble; urgency=medium
+
+  * Merge with Debian experimental, remaining change:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Sat, 24 Feb 2024 23:33:04 +0300
+
 qtbase-opensource-src (5.15.12+dfsg-3) experimental; urgency=medium
 
   * Merge 5.15.10+dfsg-7 upload from unstable.
@@ -157,6 +252,13 @@ qtbase-opensource-src (5.15.12+dfsg-2) e
 
  -- Dmitry Shachnev <mitya57@debian.org>  Sun, 14 Jan 2024 13:23:36 +0300
 
+qtbase-opensource-src (5.15.12+dfsg-1ubuntu1) noble; urgency=medium
+
+  * Merge with Debian experimental, remaining change:
+    - Force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on start.
+
+ -- Dmitry Shachnev <mitya57@ubuntu.com>  Tue, 26 Dec 2023 10:42:00 +0300
+
 qtbase-opensource-src (5.15.12+dfsg-1) experimental; urgency=medium
 
   * New upstream release.
@@ -207,6 +309,13 @@ qtbase-opensource-src (5.15.10+dfsg-6) u
 
  -- Dmitry Shachnev <mitya57@debian.org>  Sat, 13 Jan 2024 19:53:52 +0300
 
+qtbase-opensource-src (5.15.10+dfsg-5ubuntu1) noble; urgency=medium
+
+  * For now force -D_FORTIFY_SOURCE=2 to avoid Qt/KDE apps crashing on
+    start.
+
+ -- Rik Mills <rikmills@kde.org>  Fri, 22 Dec 2023 10:40:00 +0000
+
 qtbase-opensource-src (5.15.10+dfsg-5) unstable; urgency=medium
 
   * Add a patch to support LoongArch (closes: #1054569). Thanks Dandan Zhang!
diff -pruN 5.15.17+dfsg-1/debian/control 5.15.17+dfsg-1ubuntu1/debian/control
--- 5.15.17+dfsg-1/debian/control	2025-05-24 19:32:13.000000000 +0000
+++ 5.15.17+dfsg-1ubuntu1/debian/control	2025-07-11 13:12:23.000000000 +0000
@@ -1,7 +1,8 @@
 Source: qtbase-opensource-src
 Section: libs
 Priority: optional
-Maintainer: Debian Qt/KDE Maintainers <debian-qt-kde@lists.debian.org>
+Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
+XSBC-Original-Maintainer: Debian Qt/KDE Maintainers <debian-qt-kde@lists.debian.org>
 Uploaders: Sune Vuorela <sune@debian.org>,
            Pino Toscano <pino@debian.org>,
            Timo Jyrinki <timo@debian.org>,
diff -pruN 5.15.17+dfsg-1/debian/libqt5core5t64.symbols 5.15.17+dfsg-1ubuntu1/debian/libqt5core5t64.symbols
--- 5.15.17+dfsg-1/debian/libqt5core5t64.symbols	2025-05-24 19:32:13.000000000 +0000
+++ 5.15.17+dfsg-1ubuntu1/debian/libqt5core5t64.symbols	2025-07-11 13:12:23.000000000 +0000
@@ -146,7 +146,7 @@ libQt5Core.so.5 libqt5core5t64 #MINVER#
  _Z5qHashdj@Qt_5 5.3.0
  (arch=!alpha !powerpc !ppc64 !ppc64el !s390x)_Z5qHashej@Qt_5 5.3.0
  _Z5qHashfj@Qt_5 5.3.0
- (arch=alpha powerpc ppc64 ppc64el s390x)_Z5qHashgj@Qt_5 5.6.1
+ (arch=alpha powerpc ppc64 s390x)_Z5qHashgj@Qt_5 5.6.1
  _Z5qQNaNv@Qt_5 5.0.2
  _Z5qSNaNv@Qt_5 5.0.2
  _Z5qdtoadPiS_@Qt_5 5.7.0
diff -pruN 5.15.17+dfsg-1/debian/patches/CVE-2025-5455.diff 5.15.17+dfsg-1ubuntu1/debian/patches/CVE-2025-5455.diff
--- 5.15.17+dfsg-1/debian/patches/CVE-2025-5455.diff	1970-01-01 00:00:00.000000000 +0000
+++ 5.15.17+dfsg-1ubuntu1/debian/patches/CVE-2025-5455.diff	2025-07-11 13:12:23.000000000 +0000
@@ -0,0 +1,30 @@
+Description: qDecodeDataUrl(): fix precondition violation in call to QByteArrayView::at()
+ It is a precondition violation to call QByteArrayView::at() with
+ size() as argument. The code used that, though, as an implicit
+ end-of-string check, assuming == ' ' and == '=' would both fail for
+ null bytes. Besides, QByteArrays (but most certainly QByteArrayViews)
+ need not be null-terminated, so this could read even past size().
+ .
+ To fix, use higher-level API (startsWith()), consuming parsed tokens
+ along the way.
+Origin: upstream, https://download.qt.io/official_releases/qt/5.15/CVE-2025-5455-qtbase-5.15.patch
+Last-Update: 2025-06-29
+
+--- a/src/corelib/io/qdataurl.cpp
++++ b/src/corelib/io/qdataurl.cpp
+@@ -76,10 +76,11 @@ Q_CORE_EXPORT bool qDecodeDataUrl(const
+         }
+ 
+         if (data.toLower().startsWith("charset")) {
+-            int i = 7;      // strlen("charset")
+-            while (data.at(i) == ' ')
+-                ++i;
+-            if (data.at(i) == '=')
++            int prefixSize = 7; // strlen("charset")
++            QLatin1String copy(data.constData() + prefixSize, data.size() - prefixSize);
++            while (copy.startsWith(QLatin1String(" ")))
++                copy = copy.mid(1);
++            if (copy.startsWith(QLatin1String("=")))
+                 data.prepend("text/plain;");
+         }
+ 
diff -pruN 5.15.17+dfsg-1/debian/patches/series 5.15.17+dfsg-1ubuntu1/debian/patches/series
--- 5.15.17+dfsg-1/debian/patches/series	2025-05-24 19:32:13.000000000 +0000
+++ 5.15.17+dfsg-1ubuntu1/debian/patches/series	2025-07-11 13:12:23.000000000 +0000
@@ -15,6 +15,7 @@ revert_statusnotifierhost_checking.diff
 dont_fallback_to_x11_tray_on_non_x11.diff
 check_dbus_tray_availability_every_time.diff
 a11y_null_checks.diff
+CVE-2025-5455.diff
 
 # Debian specific.
 no_htmlinfo_example.diff
diff -pruN 5.15.17+dfsg-1/debian/rules 5.15.17+dfsg-1ubuntu1/debian/rules
--- 5.15.17+dfsg-1/debian/rules	2025-05-24 19:32:13.000000000 +0000
+++ 5.15.17+dfsg-1ubuntu1/debian/rules	2025-07-11 13:12:23.000000000 +0000
@@ -71,6 +71,8 @@ else
 	NUMJOBS = 1
 endif
 
+export DEB_CPPFLAGS_MAINT_APPEND = -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2
+
 %:
 	dh $@ --with pkgkde_symbolshelper
 
