ICSA-21-350-12: Siemens SIMATIC ITC

CISA's summary

Summary: Multiple LibVNC vulnerabilities in the affected products listed below could allow remote code execution, information disclosure and Denial-of-Service attacks under certain conditions. Siemens has released updates for the affected products and recommends to update to the latest versions.

Products, as the advisory lists them

DeSpy has not checked any unit, hardware revision or firmware.

Vulnerabilities in this advisory

• CVE-2017-18922 — CVE-2017-18922 · CWE-787

  websockets.c in LibVNCServer prior to 0.9.12 did not properly decode certain WebSocket frames. A malicious attacker could exploit this by sending specially crafted WebSocket frames to a server, causing a heap-based buffer overflow.

• CVE-2018-20019 — CVE-2018-20019 · CWE-787

  LibVNC before commit a83439b9fbe0f03c48eb94ed05729cb016f8b72f contains multiple heap out-of-bound write vulnerabilities in VNC client code that can result remote code execution.

• CVE-2018-20748 — CVE-2018-20748 · CWE-787

  LibVNC before 0.9.12 contains multiple heap out-of-bounds write vulnerabilities in libvncclient/rfbproto.c. The fix for CVE-2018-20019 was incomplete.

• CVE-2018-20749 — CVE-2018-20749 · CWE-787

  LibVNC before 0.9.12 contains a heap out-of-bounds write vulnerability in libvncserver/rfbserver.c. The fix for CVE-2018-15127 was incomplete.

• CVE-2018-20750 — CVE-2018-20750 · CWE-787

  LibVNC through 0.9.12 contains a heap out-of-bounds write vulnerability in libvncserver/rfbserver.c. The fix for CVE-2018-15127 was incomplete.

• CVE-2018-21247 — CVE-2018-21247 · CWE-200

  An issue was discovered in LibVNCServer before 0.9.13. There is an information leak (of uninitialized memory contents) in the libvncclient/rfbproto.c ConnectToRFBRepeater function.

• CVE-2019-15681 — CVE-2019-15681 · CWE-665

  LibVNC commit before d01e1bb4246323ba6fcee3b82ef1faa9b1dac82a contains a memory leak (CWE-655) in VNC server code, which allow an attacker to read stack memory and can be abused for information disclosure. Combined with another vulnerability, it can be used to leak stack memory and bypass ASLR. This attack appear to be exploitable via network connectivity. These vulnerabilities have been fixed in commit d01e1bb4246323ba6fcee3b82ef1faa9b1dac82a.

• CVE-2019-15690 — CVE-2019-15690 · CWE-190

  A flaw was found in libvncserver. An integer overflow within the HandleCursorShape() function can be exploited to cause a heap-based buffer overflow by tricking a user or application using libvncserver to connect to an unstrusted server and subsequently send cursor shapes with specially crafted dimensions. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.

• CVE-2019-20788 — CVE-2019-20788 · CWE-190

  libvncclient/cursor.c in LibVNCServer through 0.9.12 has a HandleCursorShape integer overflow and heap-based buffer overflow via a large height or width value. NOTE: this may overlap CVE-2019-15690.

• CVE-2019-20839 — CVE-2019-20839 · CWE-120

  libvncclient/sockets.c in LibVNCServer before 0.9.13 has a buffer overflow via a long socket filename.

• CVE-2019-20840 — CVE-2019-20840 · CWE-119

  An issue was discovered in LibVNCServer before 0.9.13. libvncserver/ws_decode.c can lead to a crash because of unaligned accesses in hybiReadAndDecode.

• CVE-2020-14396 — CVE-2020-14396 · CWE-476

  An issue was discovered in LibVNCServer before 0.9.13. libvncclient/tls_openssl.c has a NULL pointer dereference.

• CVE-2020-14397 — CVE-2020-14397 · CWE-476

  An issue was discovered in LibVNCServer before 0.9.13. libvncserver/rfbregion.c has a NULL pointer dereference.

• CVE-2020-14398 — CVE-2020-14398 · CWE-835

  An issue was discovered in LibVNCServer before 0.9.13. An improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c.

• CVE-2020-14401 — CVE-2020-14401 · CWE-190

  An issue was discovered in LibVNCServer before 0.9.13. libvncserver/scale.c has a pixel_value integer overflow.

• CVE-2020-14402 — CVE-2020-14402 · CWE-119

  An issue was discovered in LibVNCServer before 0.9.13. libvncserver/corre.c allows out-of-bounds access via encodings.

• CVE-2020-14403 — CVE-2020-14403 · CWE-119

  An issue was discovered in LibVNCServer before 0.9.13. libvncserver/hextile.c allows out-of-bounds access via encodings.

• CVE-2020-14404 — CVE-2020-14404 · CWE-119

  An issue was discovered in LibVNCServer before 0.9.13. libvncserver/rre.c allows out-of-bounds access via encodings.

• CVE-2020-14405 — CVE-2020-14405 · CWE-770

  An issue was discovered in LibVNCServer before 0.9.13. libvncclient/rfbproto.c does not limit TextChat size.

Acknowledgments, as the advisory lists them

• Siemens ProductCERT: reporting these vulnerabilities to CISA.

The advisory's legal notice

Siemens Security Advisories are subject to the terms and conditions contained in Siemens' underlying license terms or other applicable agreements previously agreed to with Siemens (hereinafter "License Terms"). To the extent applicable to information, software or documentation made available in or through a Siemens Security Advisory, the Terms of Use of Siemens' Global Website (https://www.siemens.com/terms_of_use, hereinafter "Terms of Use"), in particular Sections 8-10 of the Terms of Use, shall apply additionally. In case of conflicts, the License Terms shall prevail over the Terms of Use.

Sources

• The advisory at cisa.gov
• The CSAF document (JSON)

DeSpy's copy of this version is dated 2026-09-28.