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258128aefe
- 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
- 009008e2f4
- 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
- dc78dee51a
Signed-off-by: Thomas Perale <thomas.perale@mind.be>
Signed-off-by: Julien Olivain <ju.o@free.fr>
75 lines
2.8 KiB
Diff
75 lines
2.8 KiB
Diff
From 009008e2f4d5a54dd71f422070df3af7b3dbc931 Mon Sep 17 00:00:00 2001
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From: Kazuma Matsumoto <269371721+y637F9QQ2x@users.noreply.github.com>
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Date: Sun, 22 Mar 2026 20:35:49 +0100
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Subject: [PATCH] libvncclient: add bounds checks to UltraZip subrectangle
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parsing
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HandleUltraZipBPP() iterates over sub-rectangles using numCacheRects
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(derived from the attacker-controlled rect.r.x) without validating
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that the pointer stays within the decompressed data buffer. A malicious
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server can set a large numCacheRects value, causing heap out-of-bounds
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reads via the memcpy calls in the parsing loop.
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Add bounds checks before reading the 12-byte subrect header and before
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advancing the pointer by the raw pixel data size. Use uint64_t for the
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raw data size calculation to prevent integer overflow on 32-bit platforms.
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Upstream: https://github.com/LibVNC/libvncserver/commit/009008e2f4d5a54dd71f422070df3af7b3dbc931
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CVE: CVE-2026-32853
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Signed-off-by: Thomas Perale <thomas.perale@mind.be>
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---
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src/libvncclient/ultra.c | 16 +++++++++++++++-
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1 file changed, 15 insertions(+), 1 deletion(-)
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diff --git a/src/libvncclient/ultra.c b/src/libvncclient/ultra.c
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index 1d3aaba6a..5633b8cbb 100644
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--- a/src/libvncclient/ultra.c
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+++ b/src/libvncclient/ultra.c
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@@ -126,6 +126,7 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
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int toRead=0;
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int inflateResult=0;
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unsigned char *ptr=NULL;
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+ unsigned char *ptr_end=NULL;
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lzo_uint uncompressedBytes = ry + (rw * 65535);
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unsigned int numCacheRects = rx;
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@@ -194,11 +195,18 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
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/* Put the uncompressed contents of the update on the screen. */
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ptr = (unsigned char *)client->raw_buffer;
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+ ptr_end = ptr + uncompressedBytes;
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for (i=0; i<numCacheRects; i++)
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{
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unsigned short sx, sy, sw, sh;
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unsigned int se;
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+ /* subrect header: sx(2) + sy(2) + sw(2) + sh(2) + se(4) = 12 bytes */
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+ if (ptr + 12 > ptr_end) {
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+ rfbClientLog("UltraZip: subrect %d header exceeds decompressed data bounds\n", i);
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+ return FALSE;
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+ }
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+
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memcpy((char *)&sx, ptr, 2); ptr += 2;
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memcpy((char *)&sy, ptr, 2); ptr += 2;
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memcpy((char *)&sw, ptr, 2); ptr += 2;
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@@ -213,8 +221,13 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
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if (se == rfbEncodingRaw)
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{
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+ uint64_t rawBytes = (uint64_t)sw * sh * (BPP / 8);
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+ if (rawBytes > (size_t)(ptr_end - ptr)) {
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+ rfbClientLog("UltraZip: subrect %d raw data exceeds decompressed data bounds\n", i);
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+ return FALSE;
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+ }
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client->GotBitmap(client, (unsigned char *)ptr, sx, sy, sw, sh);
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- ptr += ((sw * sh) * (BPP / 8));
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+ ptr += (size_t)rawBytes;
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}
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}
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@@ -222,3 +235,4 @@ HandleUltraZipBPP (rfbClient* client, int rx, int ry, int rw, int rh)
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}
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#undef CARDBPP
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+
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