6.7 CVE-2026-48981
pam_usb provides hardware authentication for Linux using ordinary removable media. In versions prior to 0.9.2, pam_usb calls xmlReadFile() with flags=0 when loading the configuration file, allowing libxml2 to process external entity references (XXE), potentially making outbound network connections or local file reads at XML parse time from the context of the authenticating process. The vulnerability requires the configuration file to contain crafted XML entity references. Since pam_usb.conf is root-owned, direct exploitation requires prior write access to the config, but the defence-in-depth impact is significant given that pam_usb.so runs in setuid contexts (sudo, su). This issue has been fixed in version 0.9.2.
https://nvd.nist.gov/vuln/detail/CVE-2026-48981
Categories
CWE-611 : Improper Restriction of XML External Entity Reference
The product processes an XML document that can contain XML entities with URIs that resolve to documents outside of the intended sphere of control, causing the product to embed incorrect documents into its output. An acronym used for the term "XML eXternal Entities" Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.) Many XML parsers and validators can be configured to disable external entity expansion. Recruiter software allows reading arbitrary files using XXE A browser control can allow remote attackers to determine the existence of files via Javascript containing XML script. XXE during SVG image conversion XXE in PHP application allows reading the application's configuration file. XXE in database server XXE in rapid web application development framework allows reading arbitrary files. XXE via XML-RPC request. XXE in office document product using RDF. XXE in web-based administration tool for database. XXE in product that performs large-scale data analysis. XXE in XSL stylesheet functionality in a common library used by some web browsers.
References
security-advisories@github.com
AFFECTED (from MITRE)
| Vendor |
Product |
Versions |
| mcdope |
pam_usb |
|
| © 2022 The MITRE Corporation. This work is reproduced and distributed with the permission of The MITRE Corporation. |
CPE
REMEDIATION
EXPLOITS
Exploit-db.com
| id |
description |
date |
|
| No known exploits |
POC Github
Other Nist (github, ...)
CAPEC
Common Attack Pattern Enumerations and Classifications
| id |
description |
severity |
| 221 |
Data Serialization External Entities Blowup
This attack takes advantage of the entity replacement property of certain data serialization languages (e.g., XML, YAML, etc.) where the value of the replacement is a URI. A well-crafted file could have the entity refer to a URI that consumes a large amount of resources to create a denial of service condition. This can cause the system to either freeze, crash, or execute arbitrary code depending on the URI. [Find target web service] The adversary must first find a web service that takes input data in the form of a serialized language such as XML or YAML. [Host malicious file on a server] The adversary will create a web server that contains a malicious file. This file will be extremely large, so that if a web service were to try to load it, the service would most likely hang. [Craft malicious data] Using the serialization language that the web service takes as input, the adversary will craft data that links to the malicious file using an external entity reference to the URL of the file. [Send serialized data containing URI] The adversary will send specially crafted serialized data to the web service. When the web service loads the input, it will attempt to download the malicious file. Depending on the amount of memory the web service has, this could either crash the service or cause it to hang, resulting in a Denial of Service attack. |
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