Home Cyber Crime HAProxy vulnerability enables HTTP request smuggling attacks

HAProxy vulnerability enables HTTP request smuggling attacks

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Adam Bannister

09 September 2021 at 15:07 UTC

Up to date: 09 September 2021 at 15:14 UTC

Undertaking maintainers patch integer overflow flaw that has varied probably damaging outcomes

HAProxy vulnerability enables HTTP request smuggling attacks

Safety researchers have disclosed a HTTP request smuggling vulnerability in HAProxy, the favored open supply load balancer.

Customers of HAProxy, which ships with most mainstream Linux distributions and is especially geared in the direction of use by excessive visitors web sites, have been urged to replace their methods.

Researchers at DevOps platform JFrog demonstrated how an integer overflow flaw (CVE-2021-40346) could be abused to carry out HTTP request smuggling assaults that bypass any entry management lists (ACLs) outlined in HAProxy.

Contingent on front- and back-end server configurations, assaults may additionally probably see adversaries hijack consumer classes, entry or modify delicate knowledge, and exploit mirrored XSS vulnerabilities with out consumer interplay, claims JFrog.

HTTP request smuggling defined

HTTP request smuggling, which first emerged in 2005, interferes with how web sites course of sequences of HTTP requests acquired from customers.

Load balancers (or reverse proxies) usually ahead a number of HTTP requests, consecutively, to back-end servers over the identical back-end network connection.

RECOMMENDED Black Hat USA: HTTP/2 flaws expose organizations to fresh wave of request smuggling attacks

If front- and back-end servers disagree concerning the boundaries separating requests then they will additionally interpret malicious, ambiguous requests divergently – with probably devastating outcomes.

Smuggling by way of integer overflow

The approach is usually executed by “supplying each the and headers with contradicting lengths in the identical request and aiming for parsing inconsistencies between the frontend and backend servers,” reads a weblog put up penned by Ori Hollander and Or Peles of JFrog-owned software program safety automation platform Vdoo.

“In our case, nonetheless, the assault was made attainable by using an integer overflow vulnerability that allowed reaching an sudden state in HAProxy whereas parsing an HTTP request – particularly – within the logic that offers with headers.”

HTTP request smuggling with HAProxyHTTP request smuggling with HAProxy

Preceded by a proof of HAProxy’s twin phases for dealing with HTTP request logic, the researchers’ detailed a bypass of safety controls wherein “HAProxy is simply conscious of a single HTTP request being forwarded and thus solely returns a single HTTP response (the primary) from the backend server again to the consumer”.

Subsequently they defined easy methods to additionally obtain the HTTP response for the smuggled request by sending two consecutive requests.

The analysis duo then outlined a possible technique of automating discovery of the flaw and comparable integer overflow vulnerabilities.

Updates and workaround

The vulnerability was mounted in HAProxy variations 2.0.25, 2.2.17, 2.3.14, and a pair of.4.4 by including dimension checks for the title and worth lengths.

Hollander and Peles supplied a workaround for customers unable to instantly apply updates that reconfigures HAProxy in such a approach that “ought to mitigate all variants of this assault that we’ve encountered”.

Request smuggling revitalized

The venerable request smuggling approach was developed additional final month when James Kettle, head of analysis at PortSwigger Net Safety (The Each day Swig’s dad or mum firm) showcased his exploits targeting HTTP/2 infrastructure at Black Hat USA 2021.

Kettle, whose 2019 Black Hat presentation additionally focused on HTTP request smuggling, customary desynchronization assaults that noticed him steal secrets and techniques from web sites working Amazon’s Software Load Balancer, poison each web page on Bitbucket, and power Atlassian to universally signal customers out of Jira.

Catch up on the latest hacking techniques

A novel different to HTTP request smuggling was acknowledged as 2020’s top web hacking technique by Kettle’s employer.

Unveiled by Bishop Fox researchers in September, HTTP/2 cleartext (H2C) smuggling “abuses H2C-unware front-ends to create a tunnel to backend methods, enabling attackers to bypass frontend rewrite guidelines and exploit inside HTTP headers,” stated Kettle in summarizing the successful entry’s impression.

Attendees at Black Hat 2020, in the meantime, have been handled to a quartet of novel variants of HTTP request smuggling assaults by Amit Klein, vp of safety analysis at SafeBreach.

RELATED HTTP request smuggling vulnerability in Apache Tomcat ‘has been present since 2015’



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