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From: Thomas Perale via buildroot <buildroot@buildroot.org>
To: buildroot@buildroot.org
Subject: [Buildroot] [PATCH] package/libvncserver: patch CVE-2026-3285{3, 4}
Date: Tue, 12 May 2026 10:10:41 +0200	[thread overview]
Message-ID: <20260512081041.85459-1-thomas.perale@mind.be> (raw)

- CVE-2026-32853:
    LibVNCServer versions 0.9.15 and prior (fixed in commit 009008e)
    contain a heap out-of-bounds read vulnerability in the UltraZip
    encoding handler that allows a malicious VNC server to cause
    information disclosure or application crash. Attackers can exploit
    improper bounds checking in the HandleUltraZipBPP() function by
    manipulating subrectangle header counts to read beyond the allocated
    heap buffer.

For more information, see:
  - https://www.cve.org/CVERecord?id=CVE-2026-32853
  - https://github.com/LibVNC/libvncserver/security/advisories/GHSA-87q7-v983-qwcj
  - https://github.com/LibVNC/libvncserver/commit/009008e2f4d5a54dd71f422070df3af7b3dbc931

- CVE-2026-32854:
    LibVNCServer versions 0.9.15 and prior (fixed in commit dc78dee)
    contain null pointer dereference vulnerabilities in the HTTP proxy
    handlers within httpProcessInput() in httpd.c that allow remote
    attackers to cause a denial of service by sending specially crafted
    HTTP requests. Attackers can exploit missing validation of strchr()
    return values in the CONNECT and GET proxy handling paths to trigger
    null pointer dereferences and crash the server when httpd and proxy
    features are enabled.

For more information, see:
  - https://www.cve.org/CVERecord?id=CVE-2026-32854
  - https://github.com/LibVNC/libvncserver/security/advisories/GHSA-xjp8-4qqv-5x4x
  - https://github.com/LibVNC/libvncserver/commit/dc78dee51a7e270e537a541a17befdf2073f5314

Signed-off-by: Thomas Perale <thomas.perale@mind.be>
---
 ...cks-to-UltraZip-subrectangle-parsing.patch | 74 +++++++++++++++++++
 ...dereferences-in-httpd-proxy-handlers.patch | 64 ++++++++++++++++
 package/libvncserver/libvncserver.mk          |  6 ++
 3 files changed, 144 insertions(+)
 create mode 100644 package/libvncserver/0002-add-bounds-checks-to-UltraZip-subrectangle-parsing.patch
 create mode 100644 package/libvncserver/0003-fix-NULL-pointer-dereferences-in-httpd-proxy-handlers.patch

diff --git a/package/libvncserver/0002-add-bounds-checks-to-UltraZip-subrectangle-parsing.patch b/package/libvncserver/0002-add-bounds-checks-to-UltraZip-subrectangle-parsing.patch
new file mode 100644
index 0000000000..fa4a7718cc
--- /dev/null
+++ b/package/libvncserver/0002-add-bounds-checks-to-UltraZip-subrectangle-parsing.patch
@@ -0,0 +1,74 @@
+From 009008e2f4d5a54dd71f422070df3af7b3dbc931 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.
+
+Upstream: https://github.com/LibVNC/libvncserver/commit/009008e2f4d5a54dd71f422070df3af7b3dbc931
+CVE: CVE-2026-32853
+Signed-off-by: Thomas Perale <thomas.perale@mind.be>
+---
+ src/libvncclient/ultra.c | 16 +++++++++++++++-
+ 1 file changed, 15 insertions(+), 1 deletion(-)
+
+diff --git a/src/libvncclient/ultra.c b/src/libvncclient/ultra.c
+index 1d3aaba6a..5633b8cbb 100644
+--- a/src/libvncclient/ultra.c
++++ b/src/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/package/libvncserver/0003-fix-NULL-pointer-dereferences-in-httpd-proxy-handlers.patch b/package/libvncserver/0003-fix-NULL-pointer-dereferences-in-httpd-proxy-handlers.patch
new file mode 100644
index 0000000000..2d3ee45be8
--- /dev/null
+++ b/package/libvncserver/0003-fix-NULL-pointer-dereferences-in-httpd-proxy-handlers.patch
@@ -0,0 +1,64 @@
+From dc78dee51a7e270e537a541a17befdf2073f5314 Mon Sep 17 00:00:00 2001
+From: Kazuma Matsumoto <269371721+y637F9QQ2x@users.noreply.github.com>
+Date: Thu, 19 Mar 2026 17:42:00 +0900
+Subject: [PATCH] libvncserver: fix NULL pointer dereferences in httpd proxy
+ handlers
+
+httpProcessInput() passes the return value of strchr() to atoi()
+and strncmp() without checking for NULL. If a CONNECT request
+contains no colon, or a GET request contains no slash, strchr()
+returns NULL, leading to a segmentation fault.
+
+Add NULL checks before using the strchr() return values.
+
+CVE: CVE-2026-32854
+Upstream: https://github.com/LibVNC/libvncserver/commit/dc78dee51a7e270e537a541a17befdf2073f5314
+Signed-off-by: Thomas Perale <thomas.perale@mind.be>
+---
+ src/libvncserver/httpd.c | 24 ++++++++++++++----------
+ 1 file changed, 14 insertions(+), 10 deletions(-)
+
+diff --git a/src/libvncserver/httpd.c b/src/libvncserver/httpd.c
+index f4fe51c9..7cefadc4 100644
+--- a/src/libvncserver/httpd.c
++++ b/src/libvncserver/httpd.c
+@@ -337,10 +337,11 @@ httpProcessInput(rfbScreenInfoPtr rfbScreen)
+ 
+ 
+     /* Process the request. */
+-    if(rfbScreen->httpEnableProxyConnect) {
++if(rfbScreen->httpEnableProxyConnect) {
+ 	const static char* PROXY_OK_STR = "HTTP/1.0 200 OK\r\nContent-Type: octet-stream\r\nPragma: no-cache\r\n\r\n";
+ 	if(!strncmp(buf, "CONNECT ", 8)) {
+-	    if(atoi(strchr(buf, ':')+1)!=rfbScreen->port) {
++	    char *colon = strchr(buf, ':');
++	    if(colon == NULL || atoi(colon+1)!=rfbScreen->port) {
+ 		rfbErr("httpd: CONNECT format invalid.\n");
+ 		rfbWriteExact(&cl,INVALID_REQUEST_STR, strlen(INVALID_REQUEST_STR));
+ 		httpCloseSock(rfbScreen);
+@@ -353,14 +354,17 @@ httpProcessInput(rfbScreenInfoPtr rfbScreen)
+ 	    rfbScreen->httpSock = RFB_INVALID_SOCKET;
+ 	    return;
+ 	}
+-	if (!strncmp(buf, "GET ",4) && !strncmp(strchr(buf,'/'),"/proxied.connection HTTP/1.", 27)) {
+-	    /* proxy connection */
+-	    rfbLog("httpd: client asked for /proxied.connection\n");
+-	    rfbWriteExact(&cl,PROXY_OK_STR,strlen(PROXY_OK_STR));
+-	    rfbNewClientConnection(rfbScreen,rfbScreen->httpSock);
+-	    rfbScreen->httpSock = RFB_INVALID_SOCKET;
+-	    return;
+-	}	   
++	if (!strncmp(buf, "GET ",4)) {
++	    char *slash = strchr(buf, '/');
++	    if (slash != NULL && !strncmp(slash,"/proxied.connection HTTP/1.", 27)) {
++		/* proxy connection */
++		rfbLog("httpd: client asked for /proxied.connection\n");
++		rfbWriteExact(&cl,PROXY_OK_STR,strlen(PROXY_OK_STR));
++		rfbNewClientConnection(rfbScreen,rfbScreen->httpSock);
++		rfbScreen->httpSock = RFB_INVALID_SOCKET;
++		return;
++	    }
++	}
+     }
+ 
+     if (strncmp(buf, "GET ", 4)) {
diff --git a/package/libvncserver/libvncserver.mk b/package/libvncserver/libvncserver.mk
index 1180fc8dc7..49c94b8708 100644
--- a/package/libvncserver/libvncserver.mk
+++ b/package/libvncserver/libvncserver.mk
@@ -13,6 +13,12 @@ LIBVNCSERVER_INSTALL_STAGING = YES
 LIBVNCSERVER_DEPENDENCIES = host-pkgconf lzo
 LIBVNCSERVER_CONF_OPTS = -DWITH_LZO=ON
 
+# 0002-add-bounds-checks-to-UltraZip-subrectangle-parsing.patch
+LIBVNCSERVER_IGNORE_CVES += CVE-2026-32853
+
+# 0003-fix-NULL-pointer-dereferences-in-httpd-proxy-handlers.patch
+LIBVNCSERVER_IGNORE_CVES += CVE-2026-32854
+
 # only used for examples
 LIBVNCSERVER_CONF_OPTS += \
 	-DWITH_FFMPEG=OFF \
-- 
2.54.0

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             reply	other threads:[~2026-05-12  8:10 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-05-12  8:10 Thomas Perale via buildroot [this message]
2026-05-12 20:42 ` [Buildroot] [PATCH] package/libvncserver: patch CVE-2026-3285{3, 4} Julien Olivain via buildroot

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