June 19, 2019 By Shane Schick 2 min read

A kernel flaw dubbed TCP SACK Panic could allow remote attackers to compromise organizations running large fleets of production Linux computers, according to a series of security advisories.

Netflix was among the first to raise alarm bells over the vulnerability, also known as CVE-2019-11477, which could potentially be used to crash a machine by triggering a kernel “panic.” The issue affects those running systems based on Linux kernel version 2.6.29 and above and is one of four known flaws. TCP SACK Panic is considered the most dangerous, researchers said.

The Scope of the SACK Panic Threat

In its own security advisory, Red Hat suggested that while the flaw could be used by cybercriminals to wage denial-of-service (DoS) attacks, it would not allow them to escalate privileges on compromised machines to steal information.

SACK refers to Selective Acknowledgment, a mechanism that has traditionally been used in Linux-based systems to ensure networks run efficiently even if there is TCP packet loss between senders and receivers. When the Socket Buffer (SKB) — a data structure within Linux TCP implementations — reaches more than 17 fragments of packet data, however, a kernel panic can cause it to crash.

Threat actors could also send specially crafted SACK packets that trigger a panic, researchers said, adding that all four of the reported flaws are interrelated. Others include SACK Slowness, also known as CVE-2019-11478, a resource consumption bug dubbed CVE-2019-11479, and another SACK slowness flaw known as CVE-2019-5599.

Stay Calm Amid the TCP SACK Panic

Flaws such as these can be addressed through software patches, but the onus is on those running vulnerable IT systems to ensure they are properly applied. Unfortunately, this doesn’t always happen as quickly and consistently as it should.

Experts have shown, for example, that many organizations would benefit from improved patch posture reporting. In other words, firms need a way to bring together all available data on what patches have been performed and whether they have remediated vulnerabilities. Tools are available to assist in this area, which may be the best way for Linux users to ensure they aren’t compromised by something like the TCP SACK Panic threat.

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