openssh

“regresshion”-vulnerability-in-openssh-gives-attackers-root-on-linux

“RegreSSHion” vulnerability in OpenSSH gives attackers root on Linux

Biz & IT, code execution, exploits, openssh, Security, vulnerabilities / /

RELAPSE —

Full system compromise possible by peppering servers with thousands of connection requests.

–

“RegreSSHion” vulnerability in OpenSSH gives attackers root on Linux

Researchers have warned of a critical vulnerability affecting the OpenSSH networking utility that can be exploited to give attackers complete control of Linux and Unix servers with no authentication required.

The vulnerability, tracked as CVE-2024-6387, allows unauthenticated remote code execution with root system rights on Linux systems that are based on glibc, an open source implementation of the C standard library. The vulnerability is the result of a code regression introduced in 2020 that reintroduced CVE-2006-5051, a vulnerability that was fixed in 2006. With thousands, if not millions, of vulnerable servers populating the Internet, this latest vulnerability could pose a significant risk.

Complete system takeover

“This vulnerability, if exploited, could lead to full system compromise where an attacker can execute arbitrary code with the highest privileges, resulting in a complete system takeover, installation of malware, data manipulation, and the creation of backdoors for persistent access,” wrote Bharat Jogi, the senior director of threat research at Qualys, the security firm that discovered it. “It could facilitate network propagation, allowing attackers to use a compromised system as a foothold to traverse and exploit other vulnerable systems within the organization.”

The risk is in part driven by the central role OpenSSH plays in virtually every internal network connected to the Internet. It provides a channel for administrators to connect to protected devices remotely or from one device to another inside the network. The ability for OpenSSH to support multiple strong encryption protocols, its integration into virtually all modern operating systems, and its location at the very perimeter of networks further drive its popularity.

Besides the ubiquity of vulnerable servers populating the Internet, CVE-2024-6387 also provides a potent means for executing malicious code stems with the highest privileges, with no authentication required. The flaw stems from faulty management of the signal handler, a component in glibc for responding to potentially serious events such as division-by-zero attempts. When a client device initiates a connection but doesn’t successfully authenticate itself within an allotted time (120 seconds by default), vulnerable OpenSSH systems call what’s known as a SIGALRM handler asynchronously. The flaw resides in sshd, the main OpenSSH engine. Qualys has named the vulnerability regreSSHion.

The severity of the threat posed by exploitation is significant, but various factors are likely to prevent it from being mass exploited, security experts said. For one, the attack can take as long as eight hours to complete and require as many as 10,000 authentication steps, Stan Kaminsky, a researcher at security firm Kaspersky, said. The delay results from a defense known as address space layout randomization, which changes the memory addresses where executable code is stored to thwart attempts to run malicious payloads.

Other limitations apply. Attackers must also know the specific OS running on each targeted server. So far, no one has found a way to exploit 64-bit systems since the number of available memory addresses is exponentially higher than those available for 32-bit systems. Further mitigating the chances of success, denial-of-service attacks that limit the number of connection requests coming into a vulnerable system will prevent exploitation attempts from succeeding.

All of those limitations will likely prevent CVE-2024-6387 from being mass exploited, researchers said, but there’s still the risk of targeted attacks that pepper a specific network of interest with authentication attempts over a matter of days until allowing code execution. To cover their tracks, attackers could spread requests through a large number of IP addresses in a fashion similar to password-spraying attacks. In this way, attackers could target a handful of vulnerable networks until one or more of the attempts succeeded.

The vulnerability affects the following:

  • OpenSSH versions earlier than 4.4p1 are vulnerable to this signal handler race condition unless they are patched for CVE-2006-5051 and CVE-2008-4109.
  • Versions from 4.4p1 up to, but not including, 8.5p1 are not vulnerable due to a transformative patch for CVE-2006-5051, which made a previously unsafe function secure.
  • The vulnerability resurfaces in versions from 8.5p1 up to, but not including, 9.8p1 due to the accidental removal of a critical component in a function.

Anyone running a vulnerable version should update as soon as practicable.

“RegreSSHion” vulnerability in OpenSSH gives attackers root on Linux Read More »

linux-maintainers-were-infected-for-2-years-by-ssh-dwelling-backdoor-with-huge-reach

Linux maintainers were infected for 2 years by SSH-dwelling backdoor with huge reach

Biz & IT, ebury, Linux, openssh, secure shell, Security, SSH, Uncategorized / /

ONGOING LINUX THREAT —

Ebury backdoors SSH servers in hosting providers, giving the malware extraordinary reach.

–

A cartoon door leads to a wall of computer code.

Infrastructure used to maintain and distribute the Linux operating system kernel was infected for two years, starting in 2009, by sophisticated malware that managed to get a hold of one of the developers’ most closely guarded resources: the /etc/shadow files that stored encrypted password data for more than 550 system users, researchers said Tuesday.

The unknown attackers behind the compromise infected at least four servers inside kernel.org, the Internet domain underpinning the sprawling Linux development and distribution network, the researchers from security firm ESET said. After obtaining the cryptographic hashes for 551 user accounts on the network, the attackers were able to convert half into plaintext passwords, likely through password-cracking techniques and the use of an advanced credential-stealing feature built into the malware. From there, the attackers used the servers to send spam and carry out other nefarious activities. The four servers were likely infected and disinfected at different times, with the last two being remediated at some point in 2011.

Stealing kernel.org’s keys to the kingdom

An infection of kernel.org came to light in 2011, when kernel maintainers revealed that 448 accounts had been compromised after attackers had somehow managed to gain unfettered, or “root,” system access to servers connected to the domain. Maintainers reneged on a promise to provide an autopsy of the hack, a decision that has limited the public’s understanding of the incident.

Besides revealing the number of compromised user accounts, representatives of the Linux Kernel Organization provided no details other than saying that the infection:

  • Occurred no later than August 12, 2011, and wasn’t detected for another 17 days
  • Installed an off-the-shelf rootkit known as Phalanx on multiple servers and personal devices belonging to a senior Linux developer
  • Modified the files that both servers and end user devices inside the network used to connect through OpenSSH, an implementation of the SSH protocol for securing remote connections.

In 2014, ESET researchers said the 2011 attack likely infected kernel.org servers with a second piece of malware they called Ebury. The malware, the firm said, came in the form of a malicious code library that, when installed, created a backdoor in OpenSSH that provided the attackers with a remote root shell on infected hosts with no valid password required. In a little less than 22 months, starting in August 2011, Ebury spread to 25,000 servers. Besides the four belonging to the Linux Kernel Organization, the infection also touched one or more servers inside hosting facilities and an unnamed domain registrar and web hosting provider.

A 47-page report summarizing Ebury’s 15-year history said that the infection hitting the kernel.org network began in 2009, two years earlier than the domain was previously thought to have been compromised. The report said that since 2009, the OpenSSH-dwelling malware has infected more than 400,000 servers, all running Linux except for about 400 FreeBSD servers, a dozen OpenBSD and SunOS servers, and at least one Mac.

Researcher Marc-Etienne M. Léveillé wrote:

In our 2014 paper, we mentioned that there was evidence that kernel.org, hosting the source code of the Linux kernel, had been a victim of Ebury. Data now at our disposal reveals additional details about the incident. Ebury had been installed on at least four servers belonging to the Linux Foundation between 2009 and 2011. It seems these servers acted as mail servers, name servers, mirrors, and source code repositories at the time of the compromise. We cannot tell for sure when Ebury was removed from each of the servers, but since it was discovered in 2011 it is likely that two of the servers were compromised for as long as two years, one for one year and the other for six months.

The perpetrator also had copies of the /etc/shadow files, which overall contained 551 unique username and hashed password pairs. The cleartext passwords for 275 of those users (50%) are in possession of the attackers. We believe that the cleartext passwords were obtained by using the installed Ebury credential stealer, and by brute force.

The researcher said in an email that the Ebury and Phalanx infections appear to be separate compromises by two unrelated threat groups. Representatives of the Linux Kernel Organization didn’t respond to emails asking if they were aware of the ESET report or if its claims were accurate. There is no indication that either infection resulted in tampering with the Linux kernel source code.

Linux maintainers were infected for 2 years by SSH-dwelling backdoor with huge reach Read More »