libvncserver: fix CVE-2026-32853

Details: https://nvd.nist.gov/vuln/detail/CVE-2026-32853

Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>
Signed-off-by: Anuj Mittal <anuj.mittal@oss.qualcomm.com>

2 files changed, 79 insertions, 1 deletions

diff --git a/meta-oe/recipes-graphics/libvncserver/libvncserver/CVE-2026-32853.patch b/meta-oe/recipes-graphics/libvncserver/libvncserver/CVE-2026-32853.patch
new file mode 100644
index 0000000000..be426932db
--- /dev/null
+++ b/meta-oe/recipes-graphics/libvncserver/libvncserver/CVE-2026-32853.patch
@@ -0,0 +1,76 @@
+From 24cac3821d1665a4ed0501e6056925ef9ee53b99 Mon Sep 17 00:00:00 2001
+From: Kazuma Matsumoto <269371721+y637F9QQ2x@users.noreply.github.com>
+Date: Sun, 22 Mar 2026 20:35:49 +0100
+Subject: [PATCH] libvncclient: add bounds checks to UltraZip subrectangle
+ parsing
+
+HandleUltraZipBPP() iterates over sub-rectangles using numCacheRects
+(derived from the attacker-controlled rect.r.x) without validating
+that the pointer stays within the decompressed data buffer. A malicious
+server can set a large numCacheRects value, causing heap out-of-bounds
+reads via the memcpy calls in the parsing loop.
+
+Add bounds checks before reading the 12-byte subrect header and before
+advancing the pointer by the raw pixel data size. Use uint64_t for the
+raw data size calculation to prevent integer overflow on 32-bit platforms.
+
+(cherry picked from commit 009008e2f4d5a54dd71f422070df3af7b3dbc931)
+
+CVE: CVE-2026-32853
+Upstream-Status: Backport [https://github.com/LibVNC/libvncserver/commit/009008e2f4d5a54dd71f422070df3af7b3dbc931]
+Signed-off-by: Ankur Tyagi <ankur.tyagi85@gmail.com>
+---
+ libvncclient/ultra.c | 16 +++++++++++++++-
+ 1 file changed, 15 insertions(+), 1 deletion(-)
+
+diff --git a/libvncclient/ultra.c b/libvncclient/ultra.c
+index 1d3aaba6..5633b8cb 100644
+--- a/libvncclient/ultra.c
++++ b/libvncclient/ultra.c
+@@ -126,6 +126,7 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
+   int toRead=0;
+   int inflateResult=0;
+   unsigned char *ptr=NULL;
++  unsigned char *ptr_end=NULL;
+   lzo_uint uncompressedBytes = ry + (rw * 65535);
+   unsigned int numCacheRects = rx;
+ 
+@@ -194,11 +195,18 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
+   
+   /* Put the uncompressed contents of the update on the screen. */
+   ptr = (unsigned char *)client->raw_buffer;
++  ptr_end = ptr + uncompressedBytes;
+   for (i=0; i<numCacheRects; i++)
+   {
+     unsigned short sx, sy, sw, sh;
+     unsigned int se;
+ 
++    /* subrect header: sx(2) + sy(2) + sw(2) + sh(2) + se(4) = 12 bytes */
++    if (ptr + 12 > ptr_end) {
++      rfbClientLog("UltraZip: subrect %d header exceeds decompressed data bounds\n", i);
++      return FALSE;
++    }
++
+     memcpy((char *)&sx, ptr, 2); ptr += 2;
+     memcpy((char *)&sy, ptr, 2); ptr += 2;
+     memcpy((char *)&sw, ptr, 2); ptr += 2;
+@@ -213,8 +221,13 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
+ 
+     if (se == rfbEncodingRaw)
+     {
++        uint64_t rawBytes = (uint64_t)sw * sh * (BPP / 8);
++        if (rawBytes > (size_t)(ptr_end - ptr)) {
++          rfbClientLog("UltraZip: subrect %d raw data exceeds decompressed data bounds\n", i);
++          return FALSE;
++        }
+         client->GotBitmap(client, (unsigned char *)ptr, sx, sy, sw, sh);
+-        ptr += ((sw * sh) * (BPP / 8));
++        ptr += (size_t)rawBytes;
+     }
+   }  
+ 
+@@ -222,3 +235,4 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
+ }
+ 
+ #undef CARDBPP
++
diff --git a/meta-oe/recipes-graphics/libvncserver/libvncserver_0.9.14.bb b/meta-oe/recipes-graphics/libvncserver/libvncserver_0.9.14.bb
index 6f271ee0d3..11efd7cc0f 100644
--- a/meta-oe/recipes-graphics/libvncserver/libvncserver_0.9.14.bb
+++ b/meta-oe/recipes-graphics/libvncserver/libvncserver_0.9.14.bb
@@ -44,7 +44,9 @@ FILES:libvncclient = "${libdir}/libvncclient.*"
 
 inherit cmake pkgconfig
 
-SRC_URI = "git://github.com/LibVNC/libvncserver;branch=master;protocol=https"
+SRC_URI = "git://github.com/LibVNC/libvncserver;branch=master;protocol=https \
+           file://CVE-2026-32853.patch \
+"
 SRCREV = "10e9eb75f73e973725dc75c373de5d89807af028"
 
 S = "${WORKDIR}/git"