Ubuntu Patches ReDoS Vulnerability in Multipart HTTP Header Parser
A regular expression flaw in the multipart library allows attackers to trigger excessive resource consumption through crafted HTTP headers. Ubuntu has released security updates to address the denial-of-service risk.
TL;DR
- Multipart library contains ambiguous regex alternation in HTTP header parsing logic
- Remote attackers can exploit the flaw to cause denial of service via resource exhaustion
- Vulnerability affects systems processing untrusted HTTP multipart requests
- Ubuntu USN-8343-1 provides patches for affected distributions
- Organizations should prioritize updates to prevent application downtime
The multipart library, commonly used for parsing HTTP multipart form data, contains a regular expression vulnerability that can be exploited to cause denial of service. An attacker can craft specific HTTP header values that trigger catastrophic backtracking in the regex engine, consuming excessive CPU and memory resources.
This type of vulnerability, known as Regular Expression Denial of Service (ReDoS), represents a significant risk for web applications and APIs that process user-supplied multipart requests without proper input validation. Ubuntu has released security notice USN-8343-1 to address this issue across affected distributions.
Technical Details of the Vulnerability
- Ambiguous regex alternation in multipart's HTTP header value parsing creates ReDoS condition
- Malformed or specially crafted header values trigger exponential backtracking in regex engine
- Vulnerability is remotely exploitable without authentication or special privileges
- Affected systems experience CPU spikes and potential service unavailability
Impact and Mitigation
- Applications using multipart library to process untrusted HTTP requests are at risk
- Attackers can launch denial-of-service attacks by sending crafted multipart requests
- Ubuntu USN-8343-1 provides patched versions for affected releases
- Organizations should apply updates promptly to maintain service availability
- Input validation and rate limiting can provide defense-in-depth protection
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