CVE-2020-26575: 
Wireshark vulnerability analysis and mitigation

In Wireshark through version 3.2.7, a vulnerability was discovered in the Facebook Zero Protocol (FBZERO) dissector that could cause an infinite loop. The vulnerability, identified as CVE-2020-26575, was discovered in October 2020 and was addressed by correcting the implementation of offset advancement in the epan/dissectors/packet-fbzero.c file (NVD, Wireshark Advisory).

The vulnerability stems from an incorrect calculation of tag_offset in the FBZERO protocol dissector. When processing certain packet structures, the tag_offset was calculated incorrectly, leading to an infinite loop condition. The issue occurred because the tag_offset was being added directly by tag_len in specific cases, causing the tvb_reported_length_remaining to always return 0. This resulted in incorrect total_tag_len calculations that could be controlled through specific TCP data frame offsets (GitLab Issue). The vulnerability has been assigned a CVSS v3.1 base score of 7.5 HIGH, with vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H (NVD).

The vulnerability could allow an attacker to cause Wireshark to consume excessive CPU resources and memory, potentially leading to a denial of service condition. This could be triggered either by injecting a malformed packet onto the network or by convincing a user to open a malicious packet trace file (Wireshark Advisory).

The vulnerability is remotely exploitable without requiring authentication. An attacker could exploit this vulnerability by crafting specific TCP packets that trigger the infinite loop condition in the FBZERO dissector. The exploit could be delivered either through network injection or through a malformed packet capture file (NVD, GitLab Issue).

The vulnerability was fixed in Wireshark versions 3.4.0 and 3.2.8. Users are strongly advised to upgrade to these or later versions. The fix involved correcting the implementation of offset advancement in the FBZERO protocol dissector (Wireshark Advisory). Various distributions have also released security updates, including Debian (Debian Advisory), Fedora (Fedora Advisory), and Gentoo (Gentoo Advisory).