Security Experts:

Hackers Find Way to Bypass Mitigation for Exploited BIG-IP Vulnerability

Researchers have found a way to bypass one of the mitigations proposed by F5 Networks for the actively exploited BIG-IP vulnerability, but malicious hackers leveraged the bypass method before its public disclosure.

F5’s BIG-IP application delivery controller (ADC), specifically its Traffic Management User Interface (TMUI) configuration utility, is affected by a critical vulnerability tracked as CVE-2020-5902. An attacker with access to the configuration interface can exploit the flaw for various purposes, including to obtain credentials and other sensitive information, intercept traffic, and execute arbitrary code and commands.

The security hole, reported to the vendor by Positive Technologies, was disclosed on July 1 and the first exploitation attempts were spotted a few days later. Attacks have increased over the past days, which is not surprising considering that several proof-of-concept (PoC) exploits have been made public and that exploitation is not difficult — the entire exploit fits in a tweet.

F5 has released patches for the vulnerability and the company has also shared some mitigations that should prevent exploitation. However, researchers Rich Mirch and Chase Dardaman of Critical Start have found a way to bypass one of the mitigations. The vendor has confirmed the mitigation bypass and a more efficient mitigation has been proposed.

However, the best way for F5 customers to protect their systems against attacks is to install the patches as soon as possible.

Mirch and Dardaman were not the only ones to identify the mitigation bypass. NCC reported that it spotted the bypass method being exploited in attacks roughly six hours before the researchers made their findings public.

CVE-2020-5902 has been exploited in the wild to obtain passwords, create web shells, and to deliver DDoS malware and various other payloads. Threat intelligence company Bad Packets reported seeing more than 3,000 vulnerable BIG-IP systems on the web, including over 1,200 in the United States and roughly 500 in China.

However, NCC said the mitigation bypass may have made roughly 6,000 devices vulnerable to attacks again.

Bad Packets says it continues to see scanning and exploitation attempts targeting systems affected by CVE-2020-5902. The company has identified vulnerable systems hosted by government agencies, healthcare providers, educational organizations, Fortune 500 companies and financial institutions.

Organizations that have not installed the patches or implemented mitigations have been told that they should assume their systems have already been compromised.

F5 has shared indicators of compromise (IoC) to help customers determine if they have been targeted. Many cybersecurity solutions providers have rolled out updates to ensure that their customers are protected against attacks.

Related: "Ticketbleed" Flaw Exposes F5 Appliances to Remote Attacks

Related: Flaw in F5 Products Allows Recovery of Encrypted Data

Related: Hidden Injection Flaws Found in BIG-IP Load Balancers

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.