Cisco Warns of regreSSHion RCE Impacting Multiple Products Guru Baran
Cisco has issued a security advisory regarding a critical remote code execution (RCE) vulnerability, dubbed “regreSSHion,” that affects multiple products.
The vulnerability tracked as CVE-2024-6387, was disclosed by the Qualys Threat Research Unit on July 1, 2024. It impacts the OpenSSH server (sshd) in glibc-based Linux systems and has the potential to allow unauthenticated attackers to gain root access to affected systems.
Vulnerability Details
The regreSSHion vulnerability is a regression of an older flaw (CVE-2006-5051) that was reintroduced in OpenSSH version 8.5p1, released in October 2020.
The flaw involves a race condition in the sshd’s SIGALRM handler, which calls functions that are not async-signal-safe, such as syslog().
An attacker can exploit this by opening multiple connections and failing to authenticate within the LoginGraceTime period, triggering the vulnerable signal handler asynchronously.
The company is actively investigating its product line to determine the full scope of impacted devices. The following table lists the affected products and their respective Cisco Bug IDs:
Product Category
Product Name
Cisco Bug ID
Fixed Release Availability
Network and Content Security Devices
Adaptive Security Appliance (ASA) Software
CSCwk61618
Firepower Management Center (FMC) Software
CSCwk61618
Firepower Threat Defense (FTD) Software
CSCwk61618
FXOS Firepower Chassis Manager
CSCwk62297
Identity Services Engine (ISE)
CSCwk61938
Secure Network Analytics
CSCwk62315
Network Management and Provisioning
Crosswork Data Gateway
CSCwk62311
7.0.0 (Aug 2024)
Cyber Vision
CSCwk62289
DNA Spaces Connector
CSCwk62273
Prime Infrastructure
CSCwk62276
Smart Software Manager On-Prem
CSCwk62288
Virtualized Infrastructure Manager
CSCwk62277
Routing and Switching – Enterprise and Service Provider
ASR 5000 Series Routers
CSCwk62248
Nexus 3000 Series Switches
CSCwk61235
Nexus 9000 Series Switches in standalone NX-OS mode
CSCwk61235
Unified Computing
Intersight Virtual Appliance
CSCwk63145
Voice and Unified Communications Devices
Emergency Responder
CSCwk63694
Unified Communications Manager
CSCwk62318
Unified Communications Manager IM & Presence Service
CSCwk63634
Unity Connection
CSCwk63494
Video, Streaming, TelePresence, and Transcoding Devices
Cisco Meeting Server
CSCwk62286
SMU – CMS 3.9.2 (Aug 2024)
Mitigation and Recommendations
Cisco recommends several steps to mitigate the risk of exploitation:
Restrict SSH Access: Limit SSH access to trusted hosts only. This can be achieved by applying infrastructure access control lists (ACLs) to prevent unauthorized access to SSH services.
Upgrade OpenSSH: Upgrade to the latest patched version of OpenSSH (9.8p1) as soon as it becomes available in the package repositories of Linux distributions.
Adjust LoginGraceTime: Set the LoginGraceTime parameter to 0 in the sshd configuration file to prevent the race condition, although this may lead to denial-of-service if all connection slots become occupied[1][6][7].
The Cisco Product Security Incident Response Team (PSIRT) knows that a proof-of-concept exploit code is available for this vulnerability. However, the exploitation requires customization, and there have been no reports of malicious use.
Cisco continues to assess all products and services for impact and will update the advisory as new information becomes available.
The regreSSHion vulnerability poses a significant risk to a wide range of Cisco products.
Customers are urged to follow Cisco’s recommendations and apply the necessary patches and mitigations to protect their systems from potential exploitation.
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