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FreeBSD : libX11 -- Multiple vulnerabilities (fe99d3ca-a63a-11e8-a7c6-54e1ad3d6335)
critical Nessus Plugin ID 112074
Language:
Synopsis
The remote FreeBSD host is missing a security-related update.Description
The freedesktop.org project reports :The functions XGetFontPath, XListExtensions, and XListFonts are vulnerable to an off-by-one override on malicious server responses.
The server replies consist of chunks consisting of a length byte followed by actual string, which is not NUL-terminated. While parsing the response, the length byte is overridden with '\0', thus the memory area can be used as storage of C strings later on. To be able to NUL-terminate the last string, the buffer is reserved with an additional byte of space. For a boundary check, the variable chend (end of ch) was introduced, pointing at the end of the buffer which ch initially points to. Unfortunately there is a difference in handling 'the end of ch'. While chend points at the first byte that must not be written to, the for-loop uses chend as the last byte that can be written to. Therefore, an off-by-one can occur.
The length value is interpreted as signed char on many systems (depending on default signedness of char), which can lead to an out of boundary write up to 128 bytes in front of the allocated storage, but limited to NUL byte(s).
If the server sends a reply in which even the first string would overflow the transmitted bytes, list[0] (or flist[0]) will be set to NULL and a count of 0 is returned. If the resulting list is freed with XFreeExtensionList or XFreeFontPath later on, the first Xfree call is turned into Xfree (NULL-1) which will most likely trigger a segmentation fault. Casting the length value to unsigned char fixes the problem and allows string values with up to 255 characters.
Solution
Update the affected package.See Also
https://lists.x.org/archives/xorg-announce/2018-August/002915.html
Plugin Details
Severity: Critical
ID: 112074
File Name: freebsd_pkg_fe99d3caa63a11e8a7c654e1ad3d6335.nasl
Version: 1.3
Type: local
Family: FreeBSD Local Security Checks
Published: 8/23/2018
Updated: 11/10/2018
Supported Sensors: Nessus
Risk Information
VPR
Risk Factor: Medium
Score: 6.7
CVSS v2
Risk Factor: High
Base Score: 7.5
Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P
CVSS v3
Risk Factor: Critical
Base Score: 9.8
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Vulnerability Information
CPE: p-cpe:/a:freebsd:freebsd:libx11, cpe:/o:freebsd:freebsd
Required KB Items: Host/local_checks_enabled, Host/FreeBSD/release, Host/FreeBSD/pkg_info
Patch Publication Date: 8/22/2018
Vulnerability Publication Date: 8/21/2018