Cisco IOS XR Software Image Verification Bypass Vulnerability

TL;DR 📌

A medium severity vulnerability has been identified in Cisco IOS XR Software that allows an authenticated local attacker to bypass image signature verification, potentially leading to the installation of unsigned software. No workarounds are available, and users are advised to update to fixed software versions.

What happened 🕵️‍♂️

A vulnerability in the installation process of Cisco IOS XR Software could allow an authenticated, local attacker with root-system privileges to bypass the software image signature verification. This flaw arises from incomplete validation of files during the installation of an .iso file. An attacker could exploit this by modifying the .iso image and installing it on the device, leading to the activation of unsigned software.

Affected products 🖥️

The following Cisco products are affected if they are running a vulnerable release of Cisco IOS XR Software:

• ASR 9000 Series Aggregation Services Routers (64-bit)
• IOS XR White box (IOSXRWBD)
• IOS XRv 9000 Routers
• Network Convergence System (NCS) 540 Series Routers (running an NCS 540-iosxr base image)
• NCS 560 Series Routers
• NCS 1000 Series (NCS 1001, NCS 1002, and NCS 1004)
• NCS 5000 Series Routers
• NCS 5500 Series Routers
• NCS 5700 Series Line Cards and Routers (running an NCS 5500 base image)
• NCS 6000 Series Routers

Fixed software 🔧

Upgrade to the first fixed release in your train (or later):

Workarounds 🧯

There are no workarounds that address this vulnerability.

Risk in context 🎯

The vulnerability has a CVSS score of 6.0, categorized as Medium severity. It requires local access and root privileges to exploit, limiting the exposure to authenticated users. However, the potential for an attacker to load unsigned software poses a significant security risk, especially in sensitive environments.

Fast facts ⚡

• Vulnerability: Cisco IOS XR Software Image Verification Bypass
• CVSS Score: 6.0 (Medium)
• Exploitation: Requires local access and root privileges
• Workarounds: None available
• Fixed Software: Updates available for affected releases

For leadership 🧭

Executive summary. Routers running affected Cisco IOS XR releases can have their signed-software protections bypassed by someone who already holds root-system access, allowing unsigned code to run on the device. There is no workaround, so this should be scheduled into the next maintenance window rather than treated as an emergency.

Why it matters:

• Affects a broad range of carrier and enterprise routing platforms including ASR 9000, NCS 540/560/1000/5000/5500/5700/6000 series and IOS XRv 9000, meaning core routing infrastructure is in scope.
• The flaw sits in the .iso installation process itself, so exploitation results in the router running unsigned software rather than merely tolerating a misconfiguration.
• Requires root-system privileges already, so it is most relevant as a second-stage step for an attacker who has already compromised administrative access to the device.
• No workaround exists, so the only mitigation path is upgrading to a fixed release.

Now / Next / Later:

• Now: Identify every device running Cisco IOS XR from the affected list and confirm which train and release each is on.
• Next: Upgrade affected devices to the first fixed release for their train (24.2.21 or 24.4.2, or migrate off 7.10, 7.11 and 24.3 to a supported fixed train) during the next change window.
• Later: Tighten and audit who holds root-system privileges on IOS XR devices, since this bypass is only reachable with that level of access already in hand.