Cisco Security Advisory
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On July 29, 2020, a research paper titled “There’s a Hole in the Boot” was made publicly available. This paper discusses a vulnerability discovered in the GRand Unified Bootloader version 2 (GRUB2) bootloader that may allow an attacker to execute arbitrary code at system boot time.
The vulnerability is due to incorrect bounds checking of certain values parsed from the GRUB2 configuration file. An attacker could exploit this vulnerability by supplying a crafted configuration file for GRUB2. When this file is processed, an exploitable buffer overflow condition may occur. A successful exploit could allow the attacker to inject arbitrary code that is executed before the operating system is loaded on the targeted system.
On systems protected by the Unified Extensible Firmware Interface (UEFI) secure boot feature, exploitation of this vulnerability may allow the attacker to tamper with the secure boot process.
Multiple Cisco products are affected by this vulnerability.
Cisco will release software updates that address this vulnerability. Any workarounds for a specific Cisco product or service will be documented in the relevant Cisco bugs, which are identified in the Vulnerable Products section of this advisory.
This advisory will be updated as additional information becomes available.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-grub2-code-exec-xLePCAPY
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The following table lists Cisco products that are affected by the vulnerability that is described in this advisory.
The Vulnerable Products section includes Cisco bug IDs for each affected product or service. The bugs are accessible through the Cisco Bug Search Tool and contain additional platform-specific information, including workarounds (if available) and fixed software releases.
Any product or service not listed in the Products Under Investigation or Vulnerable Products section of this advisory is to be considered not vulnerable. Because this is an ongoing investigation, please be aware that products and services that are currently considered not vulnerable may subsequently be considered vulnerable as additional information becomes available.
Vulnerable Products
This vulnerability affects Cisco Products if they implement a vulnerable release of the GRUB2 bootloader and do not validate the GRUB2 configuration file.
The following table lists Cisco products that are affected by the vulnerability that is described in this advisory. If a future release date is indicated for software, the date provided represents an estimate based on all information known to Cisco as of the Last Updated date at the top of the advisory. Availability dates are subject to change based on a number of factors, including satisfactory testing results and delivery of other priority features and fixes. If no version or date is listed for an affected component (indicated by a blank field and/or an advisory designation of Interim), Cisco is continuing to evaluate the fix and will update the advisory as additional information becomes available. After the advisory is marked Final, customers should refer to the associated Cisco bug(s) for further details.
Product Cisco Bug ID Fixed Release Availability Routing and Switching - Enterprise and Service Provider Cisco Cloud Services Router 1000V Series CSCvv04959 Cisco Integrated Services Virtual Router (ISRv) CSCvv04959 Network and Content Security Devices Cisco Identity Services Engine (ISE) CSCvv04957 Unified Computing Cisco Enterprise NFV Infrastructure Software (NFVIS) CSCvv05161 Products Confirmed Not Vulnerable
Only products and services listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.
Cisco has confirmed that this vulnerability does not affect the following products and services.
Network and Content Security Devices
- Cisco Firepower Management System
Routing and Switching - Enterprise and Service Provider
- Cisco 1000 Series Connected Grid Routers
- Cisco IR800 Series Integrated Services Routers (ISRs)
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This vulnerability affects Cisco devices that integrate a vulnerable release of the GRUB2 bootloader. The bootloader is software that is executed during the system startup process; it is initialized by the system firmware and performs the necessary initialization for loading the operating system. GRUB2 reads its configuration parameters from a text file. An affected version of GRUB2 improperly performs the bounds checking of specific values parsed from the configuration file.
An attacker who can modify this configuration file (by possessing either administrative privileges to the device or physical access to the targeted system) could exploit this vulnerability by supplying a crafted configuration file for GRUB2. When this file is processed, a heap-based buffer overflow may occur. The attacker could use this vulnerability to achieve arbitrary code execution in the preboot environment of an affected system.
Exploitation of this vulnerability would require an attacker to modify the GRUB2 configuration file. Most Cisco devices validate the GRUB2 configuration file during the boot process. An attempt to exploit this vulnerability will cause the digital signature check to fail. When this check fails, the Cisco device will not let that software boot, thereby preventing the malicious code from running.
On a subset of Cisco devices, the GRUB2 configuration file is not validated. These products are affected by the vulnerability described in this advisory, and listed in Vulnerable Products section.
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Any workarounds for a specific Cisco product or service will be documented in the relevant Cisco bugs, which are identified in the Vulnerable Products section of this advisory.
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For information about fixed software releases, consult the Cisco bugs identified in the Vulnerable Products section of this advisory.
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
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The Cisco Product Security Incident Response Team (PSIRT) is aware that proof-of-concept exploit code is available for the vulnerability described in this advisory.
The Cisco PSIRT is not aware of any malicious use of the vulnerability that is described in this advisory.
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Cisco would like to thank Mickey Shkatov and Jesse Michael of Eclypsium for reporting this vulnerability.
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To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
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Show LessVersion Description Section Status Date 1.1 Updated the summary and moved the product under investigation to the list of vulnerable products. Summary, Affected Products Interim 2020-AUG-10 1.0 Initial public release. — Interim 2020-AUG-04
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