Vulnerabilities > CVE-2019-12649 - Improper Verification of Cryptographic Signature vulnerability in Cisco IOS and IOS XE
Attack vector
LOCAL Attack complexity
LOW Privileges required
HIGH Confidentiality impact
HIGH Integrity impact
HIGH Availability impact
HIGH Summary
A vulnerability in the Image Verification feature of Cisco IOS XE Software could allow an authenticated, local attacker to install and boot a malicious software image or execute unsigned binaries on an affected device. The vulnerability exists because, under certain circumstances, an affected device can be configured to not verify the digital signatures of system image files during the boot process. An attacker could exploit this vulnerability by abusing a specific feature that is part of the device boot process. A successful exploit could allow the attacker to install and boot a malicious software image or execute unsigned binaries on the targeted device.
Vulnerable Configurations
Common Weakness Enumeration (CWE)
Common Attack Pattern Enumeration and Classification (CAPEC)
- Padding Oracle Crypto Attack An attacker is able to efficiently decrypt data without knowing the decryption key if a target system leaks data on whether or not a padding error happened while decrypting the ciphertext. A target system that leaks this type of information becomes the padding oracle and an attacker is able to make use of that oracle to efficiently decrypt data without knowing the decryption key by issuing on average 128*b calls to the padding oracle (where b is the number of bytes in the ciphertext block). In addition to performing decryption, an attacker is also able to produce valid ciphertexts (i.e., perform encryption) by using the padding oracle, all without knowing the encryption key. Any cryptosystem can be vulnerable to padding oracle attacks if the encrypted messages are not authenticated to ensure their validity prior to decryption, and then the information about padding error is leaked to the attacker. This attack technique may be used, for instance, to break CAPTCHA systems or decrypt/modify state information stored in client side objects (e.g., hidden fields or cookies). This attack technique is a side-channel attack on the cryptosystem that uses a data leak from an improperly implemented decryption routine to completely subvert the cryptosystem. The one bit of information that tells the attacker whether a padding error during decryption has occurred, in whatever form it comes, is sufficient for the attacker to break the cryptosystem. That bit of information can come in a form of an explicit error message about a padding error, a returned blank page, or even the server taking longer to respond (a timing attack). This attack can be launched cross domain where an attacker is able to use cross-domain information leaks to get the bits of information from the padding oracle from a target system / service with which the victim is communicating. To do so an attacker sends a request containing ciphertext to the target system. Due to the browser's same origin policy, the attacker is not able to see the response directly, but can use cross-domain information leak techniques to still get the information needed (i.e., information on whether or not a padding error has occurred). For instance, this can be done using "img" tag plus the onerror()/onload() events. The attacker's JavaScript can make web browsers to load an image on the target site, and know if the image is loaded or not. This is 1-bit information needed for the padding oracle attack to work: if the image is loaded, then it is valid padding, otherwise it is not.
Nessus
| NASL family | CISCO |
| NASL id | CISCO-SA-20190925-IOSXE-DIGSIG-BYPASS.NASL |
| description | According to its self-reported version, Cisco IOS XE Software is affected by a vulnerability that could result in the loading of unsigned firmware on boot. An authenticated attacker could exploit this flaw to load malicious firmware onto the device. (cisco-sa-20190925-iosxe-digsig-bypass) |
| last seen | 2020-03-17 |
| modified | 2020-03-13 |
| plugin id | 134562 |
| published | 2020-03-13 |
| reporter | This script is Copyright (C) 2020 and is owned by Tenable, Inc. or an Affiliate thereof. |
| source | https://www.tenable.com/plugins/nessus/134562 |
| title | Cisco IOS XE Software Digital Signature Verification Bypass Vulnerability |
| code | |