In TigerVNC before 1.16.2, Image.cxx in x0vncserver allows other users to observe or manipulate the screen contents, or cause an application crash, because of incorrect permissions.

A buffer overflow vulnerability in ModifiablePixelBuffer::fillRect in vncviewer was found allowing malicious VNC server to send crafted RRE message and possibly take control of the TigerVNC viewer.

Upstream patch:

https://github.com/TigerVNC/tigervnc/commit/18c020124ff1b2441f714da2017f63dba50720ba

PR:

https://github.com/TigerVNC/tigervnc/pull/399

Reference:

http://seclists.org/oss-sec/2017/q1/166

A heap-based buffer overflow was found in the way vncviewer rendered certain screen images from a vnc server. If a user could be tricked into connecting to a malicious vnc server, it may cause the vncviewer to crash, or could possibly execute arbitrary code with the permissions of the user running it.

This issue was discovered by Tim Waugh of Red Hat. Tigervnc is affected by same thing as in CVE-2014-6052. A NULL pointer dereference flaw was reported in tigervnc. A malicious VNC server could use this flaw to cause a client to crash.

In TigerVNC (VNCSConnectionST.cxx VNCSConnectionST::fence), an authenticated client can cause a double free, leading to a crash of the TigerVNC server.

Upstream patch:

https://github.com/TigerVNC/tigervnc/pull/438/commits/f3afa24da144409a3c3a0e35913112583d987671

Upstream bug:

https://github.com/TigerVNC/tigervnc/issues/437

In rfb/CSecurityTLS.cxx and rfb/CSecurityTLS.java in TigerVNC before 1.11.0, viewers mishandle TLS certificate exceptions. They store the certificates as authorities, meaning that the owner of a certificate could impersonate any server after a client had added an exception.

A flaw was found in the X.Org server. The cursor code in both Xephyr and Xwayland uses the wrong type of private at creation. It uses the cursor bits type with the cursor as private, and when initiating the cursor, that overwrites the XSELINUX context.

A heap overflow flaw was found in X.Org and Xwayland. The computation of the length in XkbSizeKeySyms() differs from what is written in XkbWriteKeySyms(), which may lead to a heap-based buffer overflow.

A buffer overflow flaw was found in X.Org and Xwayland. If XkbChangeTypesOfKey() is called with a 0 group, it will resize the key symbols table to 0 but leave the key actions unchanged. If the same function is later called with a non-zero value of groups, this will cause a buffer overflow because the key actions are of the wrong size.

A buffer overflow flaw was found in X.Org and Xwayland. The code in XkbVModMaskText() allocates a fixed-sized buffer on the stack and copies the names of the virtual modifiers to that buffer. The code fails to check the bounds of the buffer and would copy the data regardless of the size.

A use-after-free flaw was found in X.Org and Xwayland. The root cursor is referenced in the X server as a global variable. If a client frees the root cursor, the internal reference points to freed memory and causes a use-after-free.

A use-after-free flaw was found in X.Org and Xwayland. When a device is removed while still frozen, the events queued for that device remain while the device is freed. Replaying the events will cause a use-after-free.

An access to an uninitialized pointer flaw was found in X.Org and Xwayland. The function compCheckRedirect() may fail if it cannot allocate the backing pixmap. In that case, compRedirectWindow() will return a BadAlloc error without validating the window tree marked just before, which leaves the validated data partly initialized and the use of an uninitialized pointer later.

An out-of-bounds write flaw was found in X.Org and Xwayland. The function GetBarrierDevice() searches for the pointer device based on its device ID and returns the matching value, or supposedly NULL, if no match was found. However, the code will return the last element of the list if no matching device ID is found, which can lead to out-of-bounds memory access.

A use-after-free flaw was found in X.Org and Xwayland. When changing an alarm, the values of the change mask are evaluated one after the other, changing the trigger values as requested, and eventually, SyncInitTrigger() is called. If one of the changes triggers an error, the function will return early, not adding the new sync object, possibly causing a use-after-free when the alarm eventually triggers.

A flaw was found in the RandR extension, where the RRChangeProviderProperty function does not properly validate input. This issue leads to an integer overflow when computing the total size to allocate.

A flaw was found in xorg-server. Querying or changing XKB button actions such as moving from a touchpad to a mouse can result in out-of-bounds memory reads and writes. This may allow local privilege escalation or possible remote code execution in cases where X11 forwarding is involved.

A flaw was found in xorg-server. A specially crafted request to RRChangeProviderProperty or RRChangeOutputProperty can trigger an integer overflow which may lead to a disclosure of sensitive information.

Integer overflow in TigerVNC allows remote VNC servers to cause a denial of service (crash) and possibly execute arbitrary code via vectors related to screen size handling, which triggers a heap-based buffer overflow, a similar issue to CVE-2014-6051.

In TigerVNC (SSecurityPlain.cxx SSecurityPlain::processMsg), unauthenticated users can crash the server by sending long usernames.

Upstream patches:

https://github.com/TigerVNC/tigervnc/pull/440/commits/62197c89e98be47a174074e4c7429c57767a4929 https://github.com/TigerVNC/tigervnc/pull/440/commits/9801c5efcf8c1774d9c807ebd5d27ac7049ad993

In TigerVNC (SSecurityVeNCrypt.cxx SSecurityVeNCrypt::SSecurityVeNCrypt), an unauthenticated client can cause a small memory leak in the server.

Upstream patch:

https://github.com/TigerVNC/tigervnc/pull/441/commits/8f3e8663b3cf57c0b62d939d6953fbfcc112aadd

A vulnerability was found in tigerVNC. The Xvnc server from tigervnc can crash when a client terminates a TLS connection early. This is due to invalid initialization/deinitialization order of the GnuTLS library.

References:

http://seclists.org/oss-sec/2017/q1/297

Upstream patch:

https://github.com/TigerVNC/tigervnc/commit/8aa4bc53206c2430bbf0c8f4b642f59a379ee649

In TigerVNC (CConnection.cxx CConnection::CConnection), an unauthenticated client can cause a small memory leak in the server.

Upstream patch:

https://github.com/TigerVNC/tigervnc/pull/436/commits/dccb5f7d776e93863ae10bbff56a45c523c6eeb0

A flaw was found in the Big Requests extension. The request length is multiplied by 4 before checking against the maximum allowed size, potentially causing an integer overflow and bypassing the size check.

A flaw was found in the X Record extension. The RecordSanityCheckRegisterClients function does not check for an integer overflow when computing request length, which allows a client to bypass length checks.

TigerVNC version prior to 1.10.1 is vulnerable to stack use-after-return, which occurs due to incorrect usage of stack memory in ZRLEDecoder. If decoding routine would throw an exception, ZRLEDecoder may try to access stack variable, which has been already freed during the process of stack unwinding. Exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.

TigerVNC version prior to 1.10.1 is vulnerable to heap buffer overflow, which occurs in TightDecoder::FilterGradient. Exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.

TigerVNC version prior to 1.10.1 is vulnerable to stack buffer overflow, which could be triggered from CMsgReader::readSetCursor. This vulnerability occurs due to insufficient sanitization of PixelFormat. Since remote attacker can choose offset from start of the buffer to start writing his values, exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.

TigerVNC version prior to 1.10.1 is vulnerable to heap buffer overflow, which could be triggered from DecodeManager::decodeRect. Vulnerability occurs due to the signdness error in processing MemOutStream. Exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.

TigerVNC version prior to 1.10.1 is vulnerable to heap buffer overflow. Vulnerability could be triggered from CopyRectDecoder due to incorrect value checks. Exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.