CVE-2021-21240 is a high-severity vulnerability affecting httplib2, a comprehensive HTTP client library for Python. This vulnerability allows a malicious server to respond with a long series of "\xa0" characters in the "www-authenticate" header, potentially leading to a Denial of Service (DoS) condition. When a client accesses such a malicious server, the parsing process can consume significant CPU resources, causing the application to become unresponsive.
The CVSS score for this vulnerability is 7.5, indicating a high severity level. The attack vector is network-based, requiring no user interaction and no privileges, making it particularly concerning for organizations utilizing this library. The urgency for defenders is high, as organizations should prioritize patching immediately.
The vulnerability was disclosed on February 8, 2021, and has been modified since its initial announcement. Version 0.19.0 of httplib2 addresses this issue by implementing a new approach to parsing authentication headers using the pyparsing library.
Due to the nature of this vulnerability and its potential impact, organizations utilizing httplib2 should ensure they are running version 0.19.0 or later to mitigate the risk of CPU exhaustion from malicious responses.
Vulnerability Details
This vulnerability is classified under CWE-400, indicating a potential for resource exhaustion. The impact of this vulnerability is particularly pronounced in availability, as the library can become unresponsive under attack.
Technical Analysis
The root cause of this vulnerability stems from inadequate handling of specific responses from malicious servers. When the httplib2 client encounters a long series of "\xa0" characters in the "www-authenticate" header, it can enter a loop while attempting to parse this data, leading to excessive CPU usage.
The attack vector is classified as network-based, and the complexity is low, meaning that even relatively unsophisticated attackers can exploit this vulnerability. There are no privileges required to exploit this vulnerability, nor is user interaction necessary.
In terms of impact, the confidentiality and integrity of the system are not affected; however, the availability impact is rated as high. Organizations relying on httplib2 should be aware of the potential for service disruption.
Risk & Impact Analysis
Risk to organizations includes potential downtime and service unavailability. Attackers may leverage this vulnerability to create a denial of service by sending crafted requests that exploit the parsing issue within httplib2.
The blast radius could extend to any application utilizing httplib2, affecting not just individual clients but potentially entire services that depend on its functionality.
Organizations should address this issue in priority patch cycle, as failure to do so could lead to significant operational impacts.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
All versions prior to vendor patch 0.19.0 are affected by this vulnerability. Organizations should ensure that they update to this version or later.
Mitigation & Remediation
To remediate this vulnerability, organizations must upgrade to httplib2 version 0.19.0 or later. If immediate patching is not possible, consider implementing network controls to limit access to the httplib2 client from untrusted sources.
Regular monitoring of application behavior and performance can help detect potential abuse of this vulnerability. Additionally, training developers on secure coding practices can help prevent similar vulnerabilities in the future.
Detection Guidance
Monitor logs for unusual CPU usage patterns that may indicate attempts to exploit this vulnerability. Additionally, watch for repeated requests to the "www-authenticate" header that could indicate probing for this vulnerability.
Behavioral anomalies in application performance can also signal exploitation attempts. Ensure that your logging and monitoring systems are configured to capture relevant application events.
AppSecure Threat Intelligence Insight
This vulnerability highlights the importance of robust input validation and proper handling of server responses. Attackers are increasingly leveraging header parsing vulnerabilities to create denial of service conditions.
Security teams should conduct regular assessments of their dependencies and ensure that they are aware of known vulnerabilities. Engaging in continuous security testing can also help identify potential weaknesses before they can be exploited.
For organizations utilizing httplib2, consulting the latest security advisories and implementing recommended patches is essential to maintaining application security.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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