Hackers Exploited Cisco SD-WAN Flaw to Plant Malware Built to Steal Encryption Keys

Hackers exploited a critical Cisco Catalyst SD-WAN flaw, fixed in February, to plant custom malware inside the systems that control an organization’s SD-WAN network.

The malware, called KeyDrift, is designed to copy the keys that encrypt traffic between sites and store them for later use, Cisco Talos said on October 28. Talos calls the attacks historical but does not specify when they occurred or whether any keys were sent.

The flaw is tracked as CVE-2026-20127 and has a CVSS score of 10.0. It allows an unauthenticated remote attacker to bypass authentication and gain administrative privileges on these control systems. On a Controller, the attacker can log in as a high-privileged internal account that is not root.

When Cisco disclosed the flaw in February, Talos tracked its exploitation as UAT-8616, a cluster of activity it said went back to at least 2023.

In Cisco’s traditional key exchange, each SD-WAN router periodically generates an AES key for its traffic and sends it to the Catalyst SD-WAN Controller (formerly vSmart). The Controller passes the keys on to other routers. A process on the Controller called vdaemon runs the encrypted control connections that carry these keys.

On a compromised Controller, a KeyDrift component called LittleFilch hooks into vdaemon and reads control messages after they are decrypted. For a preset list of edge routers, it pulls out their IP addresses and a 32-byte field. Talos assesses that field as the AES-256 key material that the Controller passes between routers.

LittleFilch encrypts what it collects with RSA and writes it to a file. It can then send that data over UDP to an address listed in a settings file, which it deletes after reading. Talos could not recover that settings file.

The group behind KeyDrift, which Talos tracks as UAT-11473, has targeted space and satellite services, defense and aerospace technology, and policy research.

The group’s infrastructure “overlaps considerably” with Silent Train, Talos assesses with high confidence. Silent Train is the name Lumen’s Black Lotus Labs uses for a network of hacked small-office, home-office, IoT and business devices.

Lumen says Volt Typhoon used the network to hide its activity. CISA, the NSA and the FBI said in 2024 that Volt Typhoon is a Chinese state-sponsored cyber group.

Talos links UAT-11473 to Volt Typhoon only through the infrastructure overlap. It does not say the two are the same group, or how UAT-11473 relates to UAT-8616, the cluster it reported in February.

Separately, Lumen said on October 28 that Volt Typhoon was exploiting CVE-2026-20127 by late 2025 and continued to exploit it after Cisco disclosed the flaw in February. Lumen does not tie that activity to KeyDrift.

KeyDrift primarily starts via modified runit scripts that Cisco SD-WAN devices use to launch their services, according to Talos. In one version, the script for the SSH service starts a loader script, conf_sshd, before the real SSH server. The conf_sshd script writes vdaemon’s process IDs to a file, and a tool called rsshd injects KeyDrift’s main module, PolyFlame, into each of those processes.

PolyFlame runs in memory inside vdaemon. It can act as a TinyShell-like backdoor that runs commands and reads and writes files, or as a relay that forwards commands between its command server and other machines. It is built to accept commands within SD-WAN control traffic, and the analyzed samples contained no hardcoded server address.

On a compromised Validator, formerly vBond, a fake aaamgr service under /etc/sv/aaamgr/ runs a packed loader, aaamgrd, that decrypts and runs PolyFlame. Cisco’s real aaamgr component is a Python package and does not normally run as a compiled service.

There are also signs of timestomping: commands the group ran copied the timestamps and permissions of existing files onto its own files.

Affected Releases and Fixes

CVE-2026-20127 affects the Catalyst SD-WAN Controller (formerly vSmart), Manager (formerly vManage), and Validator (formerly vBond), regardless of their configuration. On-premises systems are affected, as are Cisco’s hosted SD-WAN cloud deployments, including the Cisco Managed and FedRAMP environments. Cisco added the Validator to its advisory on June 16.

Cisco says it is aware of limited exploitation of the flaw. There is no workaround, and the first fixed releases are:

Releases earlier than 20.9 and the 20.11, 20.13, 20.14 and 20.16 trains have reached end of software maintenance.

Until they can upgrade, on-premises customers can limit access to ports 22 and 830 to the IP addresses of known controllers and other known systems. Cisco says this step worked in a test environment, but that customers should check how well it works in their own networks. Such guardrails are already in place for Cisco’s hosted SD-WAN cloud deployments.

Blocking the ports does not remove malware already on a device.

Checking for KeyDrift

Talos advises organizations to install Cisco’s fixes, follow Cisco’s Catalyst SD-WAN hardening guide and watch for signs of post-compromise activity. Anyone who finds such signs should start incident response and can ask Cisco’s Technical Assistance Center (TAC) for help.

That advice does not say whether upgrading removes KeyDrift from a device that was already compromised, or whether any keys should be replaced. Cisco’s February remediation guide for this flaw warns that there could be “existing exploits which are still in place” from before an upgrade.

KeyDrift uses these files and locations, some given only by name:

• File: the run script under etc/sv/sshd/, modified to start conf_sshd
• Directory: /etc/sv/aaamgr/, a fake service on a compromised Validator
• File: aaamgrd, the packed loader
• File: conf_sshd, the loader script
• File: rsshd, the injector
• File: libdssl.so, PolyFlame
• File: libcommon.so, LittleFilch
• File: /tmp/system-vdaemon, the list of vdaemon process IDs
• File: /var/tmp/vdaemon.bin, LittleFilch’s encrypted records
• File: /var/tmp/vdaemon.conf, LittleFilch’s send settings, deleted after reading

Talos’s report does not include a list of file hashes, IP addresses or domains for KeyDrift.

Talos released Snort rules on October 28 that look for inbound KeyDrift command-and-control connections: 67387 through 67416 for Snort 2, and 7:44 through 7:73 for Snort 3. Rules 65938 and 65958, already available, cover CVE-2026-20127 itself.

The October 28 rule update lists the Snort 2 rules as disabled by default, so users of the paid Snort Subscriber rule set must turn them on. The Snort 3 rules appear with no default state.

To check for exploitation of the flaw itself, Cisco says to look in /var/log/auth.log for Accepted publickey for vmanage-admin entries from unknown IP addresses. Before opening a TAC case, customers should run request admin-tech on each control component. The remediation guide also recommends rescanning those admin-tech files with the Check Bug Applicability feature on the Bug Search Tool page for bug CSCws52722.

For US federal civilian agencies, CISA’s February 25 emergency directive sets out what to do if a root account compromise is found. They must report it to CISA, deploy fresh Manager, Controller and Validator instances from patched images, and move their edge routers to the new systems.