"Disappearing" implants, followed by first fixes for exploited Cisco IOS XE zero-day
Vulnerabilities mentionedAll →
| CVE | Vulnerability | CVSS | EPSS | Flags | Affected | Exposure | Published |
|---|---|---|---|---|---|---|---|
| CVE-2021-1435 | A vulnerability in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker to inject arbitrary commands that can be executed as the ro A vulnerability in the web UI of Cisco IOS XE Software could allow an authenticated, remote attacker to inject arbitrary commands that can be executed as the root user. This vulnerability is due to insufficient input validation. An attacker could exploit this vulnerability by sending a crafted request to the web UI of an affected device with arbitrary commands injected into a portion of the request. A successful exploit could allow the attacker to execute arbitrary commands as the root user. NVD description · AI analysis pending | 7.2 | 8% |
| — | ||
| CVE-2023-20198 | Unauthenticated Privilege Escalation in Cisco IOS XE Web UI (Actively Exploited) CVE-2023-20198 is a critical (CVSS 10.0) unauthenticated privilege escalation flaw in the web UI of Cisco IOS XE software, triggered by sending crafted network requests to the exposed web management interface. An attacker with no credentials can use the flaw to gain initial access and issue a privilege 15 command, creating a local user with normal login access; the attacker then chained CVE-2023-20273 (CVSS 7.2) to elevate that account to root and write an implant to the file system. Successful exploitation yields full administrative control of the device, including persistence via the planted implant, on Cisco IOS XE devices with the web UI enabled and reachable from the internet or untrusted networks, including Rockwell Automation Allen-Bradley Stratix 5200 and 5800 switches running IOS XE. Exploitation is confirmed in the wild: the flaw was added to CISA's KEV on 2023-10-16 with a BOD 23-02 directive, EPSS stands at 99.6% (100th percentile), and ongoing campaigns (including the 'BADCANDY' activity flagged by Australia's ASD and Cisco-related telecom intrusions attributed to Salt Typhoon) have been reported. Do: Upgrade affected devices to the fixed releases listed in Cisco's advisory (use Cisco's Software Checker) and, as immediate mitigation, disable the web UI or restrict it to trusted networks/addresses only. Check for compromise by looking for unexpected local user accounts and the implant artifacts Cisco identified (unexpected cisco_tac_alarm.log and cisco_tac.log files in /tmp or /usr/binos/conf), and immediately report positive findings to CISA per BOD 23-02. Keep in mind that patching alone does not remove a root implant, so devices with evidence of compromise should be reimaged or otherwise cleaned per vendor instructions. | 10.0 | 100% | KEV |
| large≈40,000–50,000 internet-exposed IOS XE devices at the time of disclosure (public scan data), within an IOS XE install base in the millions | |
| CVE-2023-20273 | Authenticated Command Injection (Root) in Cisco IOS XE Web UI CVE-2023-20273 is an OS command injection flaw (CWE-78) in the web UI feature of Cisco IOS XE Software, caused by insufficient input validation. An authenticated, remote attacker triggers it by sending crafted input to the web UI, and a successful exploit injects commands that run on the underlying operating system with root privileges, yielding full device compromise (in the October 2023 mass-exploitation campaign it was typically chained with the unauthenticated CVE-2023-20198 to obtain initial access and install a persistent implant). Any Cisco IOS XE device with the web UI enabled and reachable from the internet or an untrusted network is affected; this data does not specify the affected release ranges, which are enumerated in Cisco's advisory. Exploitation is confirmed in the wild: CISA added the flaw to the KEV on 2023-10-23 with BOD 23-02 response actions, EPSS is ~90% (100th percentile), and IOS XE edge devices remain recurring targets of Chinese-nexus espionage campaigns (e.g., Salt Typhoon activity against telecoms). Do: Upgrade affected devices to a fixed IOS XE release per Cisco's advisory; as an interim mitigation, disable the HTTP/HTTPS server (ip http server / ip https server) or restrict Web UI access to trusted hosts only. Per BOD 23-02, hunt for compromise on any exposed device — check for unexpected level-15 local accounts and the implant.lua backdoor in flash memory — and immediately report positive findings to CISA. | 7.2 | 90% | KEV |
| mass≈100,000+ internet-exposed IOS XE devices (public scans observed ~40,000+ compromised within days of disclosure) |
Full article619 words · extracted from helpnetsecurity.com · click to collapse
Cisco has released the first fixes for the IOS XE zero-day (CVE-2023-20198) exploited by attackers to ultimately deliver a malicious implant.
The fixes were made available on Sunday, but a curious thing happened the day before: several cybersecurity companies and organizations have noticed a drastic reduction in the number of internet-facing Cisco devices that saddled with the implant.
The reason behind that change is still unclear, but several theories have been put forward.
The attackers leveraged two zero-days (CVE-2023-20273)
On October 16, Cisco revealed that attackers have been spotted exploiting one previously unknown vulnerability (CVE-2023-20198) and an older one (CVE-2021-1435) in the web UI of Cisco IOS XE software to create highest-privilege accounts and install an implant/backdoor on internet-facing network devices.
On October 20, (i.e., past Friday), the company amended their findings and confirmed that the attackers did not, in fact, exploit CVE-2021-1435.
“It was investigated early on because a Snort signature fired early (it was seen in the telemetry), but as more information was gathered on the exploit it was determined it was not correlated,” a Cisco spokesperson told Help Net Security.
Instead, the attackers leveraged a zero-day (CVE-2023-20273) in another component of the WebUI feature to run the implant.
The implant is not able to persist a reboot, the company said, but the accounts created by the attackers must be revoked/invalidated by enterprise defenders to remove the possibility of renewed access by the threat actors.
CVE-2023-20198 fixes released
Cisco has shared indicators of compromise to help security teams detect whether their organizations’ devices have been compromised.
The first fixed release for Cisco IOS XE is now available, but fixes only CVE-2023-20198, the flaw that allows the creation of high-privilege accounts (i.e., admin accounts).
Until the other fixes are released, organizations are urged to disable the HTTP Server feature to eliminate the attack vector for these vulnerabilities.
Make sure your devices haven’t been compromised
After the public announcement of the attacks in progress, cybersecurity firms scanned the internet for reachable devices that appear to have the backdoor installed and found between 40,000 and 50,000 of them.
On Saturday, though, most of those implants couldn’t be detected anymore.
While it’s possible that many organizations have simply rebooted their Cisco devices to quickly remove the non-persistent implant, it’s unlikely that it happened so quickly and at such a scale.
CERT Orange Cyberdefense posited that someone has been cleaning up the implant’s traces on a massive scale. A coordinated action by the attackers – or maybe law enforcement or a white-hat hacker – seems the most plausible theory.
“We already received trusted intel about this cleaning step – but not on a massive way,” Orange Cyberdefense security experts noted.
“We have to assume that equipments where the implant was here till yesterday – but no longer today, are still corrupt – and are maybe in another exploitation stage,” they added, and advised organizations to investigate to make sure that no malicious users have been added to their devices and that their configuration has not been altered.
UPDATE (October 24, 2023, 03:20 a.m. ET):
After uncovering a new variant that hinders identification of compromised systems, Cisco has updated the security advisory with new guidance to detect the presence of the implant, a Cisco spokesperson told Help Net Security.
“[The implant] has been altered to check for an Authorization HTTP header value before responding,” Fox-IT researchers shared on Monday.
“This explains the much discussed plummet of identified compromised systems in recent days. Using a different fingerprinting method, Fox-IT identifies 37890 Cisco devices that remain compromised.”
UPDATE: October 31, 06:30 a.m. ET
A PoC exploit for CVE-2023-20198 has been published. Cisco has rolled out most of the fixed releases.
Text extracted automatically; images, tables and formatting may be missing. Original: https://www.helpnetsecurity.com/2023/10/23/disappearing-implants-cve-2023-20198-fixes/