Cisco Warns regreSSHion RCE

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.

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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.

Cisco has identified several products across various categories affected by this vulnerability.

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 CategoryProduct NameCisco Bug IDFixed Release Availability
Network and Content Security DevicesAdaptive Security Appliance (ASA) SoftwareCSCwk61618
Firepower Management Center (FMC) SoftwareCSCwk61618
Firepower Threat Defense (FTD) SoftwareCSCwk61618
FXOS Firepower Chassis ManagerCSCwk62297
Identity Services Engine (ISE)CSCwk61938
Secure Network AnalyticsCSCwk62315
Network Management and ProvisioningCrosswork Data GatewayCSCwk623117.0.0 (Aug 2024)
Cyber VisionCSCwk62289
DNA Spaces ConnectorCSCwk62273
Prime InfrastructureCSCwk62276
Smart Software Manager On-PremCSCwk62288
Virtualized Infrastructure ManagerCSCwk62277
Routing and Switching – Enterprise and Service ProviderASR 5000 Series RoutersCSCwk62248
Nexus 3000 Series SwitchesCSCwk61235
Nexus 9000 Series Switches in standalone NX-OS modeCSCwk61235
Unified ComputingIntersight Virtual ApplianceCSCwk63145
Voice and Unified Communications DevicesEmergency ResponderCSCwk63694
Unified Communications ManagerCSCwk62318
Unified Communications Manager IM & Presence ServiceCSCwk63634
Unity ConnectionCSCwk63494
Video, Streaming, TelePresence, and Transcoding DevicesCisco Meeting ServerCSCwk62286SMU – 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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Gurubaran is a co-founder of Cyber Security News and GBHackers On Security. He has 10+ years of experience as a Security Consultant, Editor, and Analyst in cybersecurity, technology, and communications.