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CVE-2018-21247

An issue was discovered in LibVNCServer before 0.9.13. There is a memory leak in the libvncclient...

7.5 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
None
Availability
None

Exploit likelihood

2.52%Up 0.9 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 7.5

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.

Record
CVE-2018-21247
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
CVSS 2.0
5.0 MediumAV:N/AC:L/Au:N/C:P/I:N/A:N
Weakness
CWE-909
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2018-21247
Updated
2026-11-02
EUVDEUVD-2018-13762 No score

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.

Record
EUVD-2018-13762
Updated
2026-11-03
GitHub AdvisoriesGHSA-355f-mpqr-3mwv 7.5

An issue was discovered in LibVNCServer before 0.9.13. There is a memory leak in the libvncclient...

An issue was discovered in LibVNCServer before 0.9.13. There is a memory leak in the libvncclient/rfbproto.c ConnectToRFBRepeater function.

Record
GHSA-355f-mpqr-3mwv
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Weakness
CWE-200, CWE-909
Updated
2026-11-02
OSV 7.5

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.

Record
CVE-2018-21247
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVDEBIAN-CVE-2018-21247 7.5

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.

Record
DEBIAN-CVE-2018-21247
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
Show 10 moreShow less
OSVRHSA-2021:1811 7.5

Red Hat Security Advisory: libvncserver security update

Record
RHSA-2021:1811
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Updated
2026-11-02
OSVRLSA-2021:1811 7.5

Moderate: libvncserver security update

LibVNCServer is a C library that enables you to implement VNC server functionality into own programs.

Security Fix(es):

  • libvncserver: uninitialized memory contents are vulnerable to Information Leak (CVE-2018-21247)

  • libvncserver: buffer overflow in ConnectClientToUnixSock() (CVE-2019-20839)

  • libvncserver: libvncserver/rfbregion.c has a NULL pointer dereference (CVE-2020-14397)

  • libvncserver: libvncclient/rfbproto.c does not limit TextChat size (CVE-2020-14405)

  • libvncserver: libvncserver/rfbserver.c has a divide by zero which could result in DoS (CVE-2020-25708)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the Rocky Linux 8.4 Release Notes linked from the References section.

Record
RLSA-2021:1811
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2018-21247 7.5

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.

Record
UBUNTU-CVE-2018-21247
CVSS 3.1
7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Updated
2026-11-02
OSVALSA-2021:1811 No score

Moderate: libvncserver security update

LibVNCServer is a C library that enables you to implement VNC server functionality into own programs.

Security Fix(es):

  • libvncserver: uninitialized memory contents are vulnerable to Information Leak (CVE-2018-21247)

  • libvncserver: buffer overflow in ConnectClientToUnixSock() (CVE-2019-20839)

  • libvncserver: libvncserver/rfbregion.c has a NULL pointer dereference (CVE-2020-14397)

  • libvncserver: libvncclient/rfbproto.c does not limit TextChat size (CVE-2020-14405)

  • libvncserver: libvncserver/rfbserver.c has a divide by zero which could result in DoS (CVE-2020-25708)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Additional Changes:

For detailed information on changes in this release, see the AlmaLinux Release Notes linked from the References section.

Record
ALSA-2021:1811
Updated
2026-11-02
OSVopenSUSE-SU-2020:0988-1 No score

Security update for LibVNCServer

This update for LibVNCServer fixes the following issues:

  • security update
  • added patches fix CVE-2018-21247 [bsc#1173874], uninitialized memory contents are vulnerable to Information leak
    • LibVNCServer-CVE-2018-21247.patch fix CVE-2019-20839 [bsc#1173875], buffer overflow in ConnectClientToUnixSock()
    • LibVNCServer-CVE-2019-20839.patch fix CVE-2019-20840 [bsc#1173876], unaligned accesses in hybiReadAndDecode can lead to denial of service
    • LibVNCServer-CVE-2019-20840.patch fix CVE-2020-14398 [bsc#1173880], improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c
    • LibVNCServer-CVE-2020-14398.patch fix CVE-2020-14397 [bsc#1173700], NULL pointer dereference in libvncserver/rfbregion.c
    • LibVNCServer-CVE-2020-14397.patch fix CVE-2020-14399 [bsc#1173743], Byte-aligned data is accessed through uint32_t pointers in libvncclient/rfbproto.c.
    • LibVNCServer-CVE-2020-14399.patch fix CVE-2020-14400 [bsc#1173691], Byte-aligned data is accessed through uint16_t pointers in libvncserver/translate.c.
    • LibVNCServer-CVE-2020-14400.patch fix CVE-2020-14401 [bsc#1173694], potential integer overflows in libvncserver/scale.c
    • LibVNCServer-CVE-2020-14401.patch fix CVE-2020-14402 [bsc#1173701], out-of-bounds access via encodings.
    • LibVNCServer-CVE-2020-14402,14403,14404.patch fix CVE-2017-18922 [bsc#1173477], preauth buffer overwrite

This update was imported from the SUSE:SLE-15:Update update project.

Record
openSUSE-SU-2020:0988-1
Updated
2026-11-02
OSVopenSUSE-SU-2020:1025-1 No score

Security update for LibVNCServer

This update for LibVNCServer fixes the following issues:

  • security update
  • added patches fix CVE-2018-21247 [bsc#1173874], uninitialized memory contents are vulnerable to Information leak
    • LibVNCServer-CVE-2018-21247.patch fix CVE-2019-20839 [bsc#1173875], buffer overflow in ConnectClientToUnixSock()
    • LibVNCServer-CVE-2019-20839.patch fix CVE-2019-20840 [bsc#1173876], unaligned accesses in hybiReadAndDecode can lead to denial of service
    • LibVNCServer-CVE-2019-20840.patch fix CVE-2020-14398 [bsc#1173880], improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c
    • LibVNCServer-CVE-2020-14398.patch fix CVE-2020-14397 [bsc#1173700], NULL pointer dereference in libvncserver/rfbregion.c
    • LibVNCServer-CVE-2020-14397.patch fix CVE-2020-14399 [bsc#1173743], Byte-aligned data is accessed through uint32_t pointers in libvncclient/rfbproto.c.
    • LibVNCServer-CVE-2020-14399.patch fix CVE-2020-14400 [bsc#1173691], Byte-aligned data is accessed through uint16_t pointers in libvncserver/translate.c.
    • LibVNCServer-CVE-2020-14400.patch fix CVE-2020-14401 [bsc#1173694], potential integer overflows in libvncserver/scale.c
    • LibVNCServer-CVE-2020-14401.patch fix CVE-2020-14402 [bsc#1173701], out-of-bounds access via encodings.
    • LibVNCServer-CVE-2020-14402,14403,14404.patch fix CVE-2017-18922 [bsc#1173477], preauth buffer overwrite

This update was imported from the SUSE:SLE-15:Update update project.

Record
openSUSE-SU-2020:1025-1
Updated
2026-11-02
OSVopenSUSE-SU-2020:1056-1 No score

Security update for LibVNCServer

This update for LibVNCServer fixes the following issues:

  • security update
  • added patches fix CVE-2018-21247 [bsc#1173874], uninitialized memory contents are vulnerable to Information leak
    • LibVNCServer-CVE-2018-21247.patch fix CVE-2019-20839 [bsc#1173875], buffer overflow in ConnectClientToUnixSock()
    • LibVNCServer-CVE-2019-20839.patch fix CVE-2019-20840 [bsc#1173876], unaligned accesses in hybiReadAndDecode can lead to denial of service
    • LibVNCServer-CVE-2019-20840.patch fix CVE-2020-14398 [bsc#1173880], improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c
    • LibVNCServer-CVE-2020-14398.patch fix CVE-2020-14397 [bsc#1173700], NULL pointer dereference in libvncserver/rfbregion.c
    • LibVNCServer-CVE-2020-14397.patch fix CVE-2020-14399 [bsc#1173743], Byte-aligned data is accessed through uint32_t pointers in libvncclient/rfbproto.c.
    • LibVNCServer-CVE-2020-14399.patch fix CVE-2020-14400 [bsc#1173691], Byte-aligned data is accessed through uint16_t pointers in libvncserver/translate.c.
    • LibVNCServer-CVE-2020-14400.patch fix CVE-2020-14401 [bsc#1173694], potential integer overflows in libvncserver/scale.c
    • LibVNCServer-CVE-2020-14401.patch fix CVE-2020-14402 [bsc#1173701], out-of-bounds access via encodings.
    • LibVNCServer-CVE-2020-14402,14403,14404.patch fix CVE-2017-18922 [bsc#1173477], preauth buffer overwrite

This update was imported from the SUSE:SLE-15:Update update project.

Record
openSUSE-SU-2020:1056-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:10598-1 No score

LibVNCServer-devel-0.9.13-3.1 on GA media

These are all security issues fixed in the LibVNCServer-devel-0.9.13-3.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:10598-1
Updated
2026-11-02
OSVSUSE-SU-2020:1922-1 No score

Security update for LibVNCServer

This update for LibVNCServer fixes the following issues:

  • security update
  • added patches fix CVE-2018-21247 [bsc#1173874], uninitialized memory contents are vulnerable to Information leak
    • LibVNCServer-CVE-2018-21247.patch fix CVE-2019-20839 [bsc#1173875], buffer overflow in ConnectClientToUnixSock()
    • LibVNCServer-CVE-2019-20839.patch fix CVE-2019-20840 [bsc#1173876], unaligned accesses in hybiReadAndDecode can lead to denial of service
    • LibVNCServer-CVE-2019-20840.patch fix CVE-2020-14398 [bsc#1173880], improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c
    • LibVNCServer-CVE-2020-14398.patch fix CVE-2020-14397 [bsc#1173700], NULL pointer dereference in libvncserver/rfbregion.c
    • LibVNCServer-CVE-2020-14397.patch fix CVE-2020-14399 [bsc#1173743], Byte-aligned data is accessed through uint32_t pointers in libvncclient/rfbproto.c.
    • LibVNCServer-CVE-2020-14399.patch fix CVE-2020-14400 [bsc#1173691], Byte-aligned data is accessed through uint16_t pointers in libvncserver/translate.c.
    • LibVNCServer-CVE-2020-14400.patch fix CVE-2020-14401 [bsc#1173694], potential integer overflows in libvncserver/scale.c
    • LibVNCServer-CVE-2020-14401.patch fix CVE-2020-14402 [bsc#1173701], out-of-bounds access via encodings.
    • LibVNCServer-CVE-2020-14402,14403,14404.patch fix CVE-2017-18922 [bsc#1173477], preauth buffer overwrite
Record
SUSE-SU-2020:1922-1
Updated
2026-11-02
OSVSUSE-SU-2020:2167-1 No score

Security update for LibVNCServer

This update for LibVNCServer fixes the following issues:

  • security update fix CVE-2018-21247 [bsc#1173874], uninitialized memory contents are vulnerable to Information leak fix CVE-2019-20839 [bsc#1173875], buffer overflow in ConnectClientToUnixSock() fix CVE-2019-20840 [bsc#1173876], unaligned accesses in hybiReadAndDecode can lead to denial of service fix CVE-2020-14398 [bsc#1173880], improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c fix CVE-2020-14397 [bsc#1173700], NULL pointer dereference in libvncserver/rfbregion.c fix CVE-2020-14399 [bsc#1173743], Byte-aligned data is accessed through uint32_t pointers in libvncclient/rfbproto.c. fix CVE-2020-14400 [bsc#1173691], Byte-aligned data is accessed through uint16_t pointers in libvncserver/translate.c. fix CVE-2020-14401 [bsc#1173694], potential integer overflows in libvncserver/scale.c fix CVE-2020-14402 [bsc#1173701], out-of-bounds access via encodings. fix CVE-2020-14403 [bsc#1173701], out-of-bounds access via encodings. fix CVE-2020-14404 [bsc#1173701], out-of-bounds access via encodings. fix CVE-2017-18922 [bsc#1173477], preauth buffer overwrite
Record
SUSE-SU-2020:2167-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
libvncserver
AlmaLinux:8
 before 0.9.11-17.el8
0.9.11-17.el8
libvncserver-devel
AlmaLinux:8
 before 0.9.11-17.el8
0.9.11-17.el8
libvncserver
Debian:12
 before 0.9.11+dfsg-1.2
0.9.11+dfsg-1.2
libvncserver
Debian:13
 before 0.9.11+dfsg-1.2
0.9.11+dfsg-1.2
libvncserver
Debian:14
 before 0.9.11+dfsg-1.2
0.9.11+dfsg-1.2
libvncserver
Debian:8
 before 0.9.9+dfsg2-6.1+deb8u4, plus listed versions
0.9.9+dfsg-6.10.9.9+dfsg2-6.1+deb8u10.9.9+dfsg2-6.1+deb8u20.9.9+dfsg2-6.1+deb8u3
0.9.9+dfsg2-6.1+deb8u4
libvncserver
Debian:9
 before 0.9.11+dfsg-1.3~deb9u1, plus listed versions
0.9.11+dfsg-10.9.11+dfsg-1+deb9u10.9.11+dfsg-1.10.9.11+dfsg-1.2
0.9.11+dfsg-1.3~deb9u1
libvncserver
Red Hat:enterprise_linux:8::appstream
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
libvncserver-debuginfo
Red Hat:enterprise_linux:8::appstream
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
libvncserver-debugsource
Red Hat:enterprise_linux:8::appstream
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
Show 42 moreShow less
Affected packages
PackageAffectedFixed
libvncserver-debuginfo
Red Hat:enterprise_linux:8::crb
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
libvncserver-debugsource
Red Hat:enterprise_linux:8::crb
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
libvncserver-devel
Red Hat:enterprise_linux:8::crb
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
libvncserver
Rocky Linux:8
 before 0:0.9.11-17.el8
0:0.9.11-17.el8
LibVNCServer
SUSE:Linux Enterprise Module for Package Hub 15 SP1
 before 0.9.10-4.22.1
0.9.10-4.22.1
LibVNCServer
SUSE:Linux Enterprise Module for Package Hub 15 SP2
 before 0.9.10-4.22.1
0.9.10-4.22.1
LibVNCServer
SUSE:Linux Enterprise Workstation Extension 15 SP1
 before 0.9.10-4.22.1
0.9.10-4.22.1
LibVNCServer
SUSE:Linux Enterprise Workstation Extension 15 SP2
 before 0.9.10-4.22.1
0.9.10-4.22.1
LibVNCServer
SUSE:HPE Helion OpenStack 8
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:OpenStack Cloud 7
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:OpenStack Cloud 8
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:OpenStack Cloud 9
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:OpenStack Cloud Crowbar 8
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:OpenStack Cloud Crowbar 9
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server for SAP Applications 12 SP2
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server for SAP Applications 12 SP3
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server for SAP Applications 12 SP4
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Software Development Kit 12 SP5
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server 12 SP2-LTSS
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server 12 SP2-BCL
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server 12 SP3-LTSS
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server 12 SP3-BCL
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server 12 SP4-LTSS
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server 12 SP5
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Linux Enterprise Server for SAP Applications 12 SP5
 before 0.9.9-17.31.1
0.9.9-17.31.1
LibVNCServer
SUSE:Enterprise Storage 5
 before 0.9.9-17.31.1
0.9.9-17.31.1
x11vnc
Ubuntu:14.04:LTS
 All versions, plus listed versions
0.9.13-1.1
 None known
libvncserver
Ubuntu:16.04:LTS
 All versions, plus listed versions
0.9.10+dfsg-30.9.10+dfsg-3build10.9.10+dfsg-3ubuntu0.16.04.10.9.10+dfsg-3ubuntu0.16.04.20.9.10+dfsg-3ubuntu0.16.04.30.9.10+dfsg-3ubuntu0.16.04.40.9.10+dfsg-3ubuntu0.16.04.50.9.10+dfsg-3ubuntu0.16.04.6
 None known
x11vnc
Ubuntu:Pro:16.04:LTS
 All versions, plus listed versions
0.9.13-1.2build10.9.13-1.2ubuntu0.1~esm1
 None known
libvncserver
Ubuntu:18.04:LTS
 All versions, plus listed versions
0.9.11+dfsg-10.9.11+dfsg-1ubuntu10.9.11+dfsg-1ubuntu1.10.9.11+dfsg-1ubuntu1.20.9.11+dfsg-1ubuntu1.30.9.11+dfsg-1ubuntu1.4
 None known
x11vnc
Ubuntu:Pro:18.04:LTS
 All versions, plus listed versions
0.9.13-20.9.13-2build10.9.13-30.9.13-3ubuntu0.1~esm1
 None known
libvncserver
Ubuntu:20.04:LTS
 All versions, plus listed versions
0.9.11+dfsg-1.30.9.12+dfsg-3ubuntu30.9.12+dfsg-60.9.12+dfsg-70.9.12+dfsg-8
Show 4 moreShow less
0.9.12+dfsg-90.9.12+dfsg-9ubuntu0.10.9.12+dfsg-9ubuntu0.20.9.12+dfsg-9ubuntu0.3
 None known
veyon
Ubuntu:20.04:LTS
 All versions, plus listed versions
4.2.4+repack1-24.2.5+repack1-14.3.1+repack1-14.3.1+repack1-24.3.1+repack1-2build14.3.1+repack1-2build2
 None known
x11vnc
Ubuntu:Pro:20.04:LTS
 All versions, plus listed versions
0.9.13-60.9.16-30.9.16-3ubuntu0.1~esm1
 None known
veyon
Ubuntu:22.04:LTS
 All versions, plus listed versions
4.5.3+repack1-1build14.5.3+repack1-1build2
 None known
veyon
Ubuntu:24.04:LTS
 All versions, plus listed versions
4.7.5+repack1-1build24.7.5+repack1-1ubuntu14.7.5+repack1-1ubuntu34.7.5+repack1-1ubuntu44.7.5+repack1-1ubuntu5
 None known
veyon
Ubuntu:25.10
 All versions, plus listed versions
4.7.5+repack1-1ubuntu64.7.5+repack1-1ubuntu74.9.7+repack1-1
 None known
veyon
Ubuntu:26.10
 All versions, plus listed versions
4.9.7+repack1-1build14.9.7+repack1-1.14.9.7+repack1-1.1build14.9.7+repack1-1.1build2
 None known
veyon
Ubuntu:26.04:LTS
 All versions, plus listed versions
4.9.7+repack1-14.9.7+repack1-1build1
 None known
LibVNCServer
openSUSE:Leap 15.1
 before 0.9.10-lp151.7.9.1
0.9.10-lp151.7.9.1
LibVNCServer
openSUSE:Leap 15.2
 before 0.9.10-lp152.9.8.1
0.9.10-lp152.9.8.1
LibVNCServer
openSUSE:Leap 15.2
 before 0.9.10-lp152.9.4.2
0.9.10-lp152.9.4.2

History

History
RecordedChangedSources
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2018-21247 is a high vulnerability (CVSS 7.5) in Libvnc Project Libvncserver, published December 25, 2018. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.52%, the 84th percentile. Fixed in libvncserver 0.9.11-17.el8.

References

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