CVE-2026-97200 in hackney
Summary
by MITRE • 10/26/2026
Allocation of Resources Without Limits or Throttling vulnerability in hackney_conn in benoitc hackney allows a malicious HTTP server to exhaust client memory via an oversized or highly compressed response body. hackney:request/5 and hackney:body/1 return the whole response body, and nothing bounds how much the connection process buffers. Any server the client requests can trigger it.
hackney_conn:read_full_body/2 and the HTTP/2 and HTTP/3 accumulators append every chunk until the body ends. With {auto_decompress, true} the buffered body is then inflated in one step with zlib:gunzip/1 or zlib:inflate/2, which return the whole output at once.
This issue affects hackney: from 2.0.0-beta.1 before 4.9.0.
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Analysis
by VulDB Data Team • 10/26/2026
The vulnerability identified as an allocation of resources without limits or throttling in the Hackney HTTP client library for Erlang/OTP represents a significant risk to application stability and availability. This flaw, tracked under CWE-770, allows a malicious HTTP server to exhaust the memory resources of the client process by sending oversized response bodies or highly compressed data that expands significantly upon decompression. The core technical issue lies in how Hackney manages connection state during body retrieval operations such as hackney:request/5 and hackney:body/1. These functions are designed to return the entire response body, but they lack any mechanism to bound the amount of memory buffered by the underlying connection process. Consequently, there is no upper limit on the size of data that can be accumulated in memory before it is processed or returned to the application layer.
The operational mechanics of this vulnerability involve specific internal functions like hackney_conn:read_full_body/2 and accumulators used for HTTP/2 and HTTP/3 protocols. These components append every incoming chunk of data until the body transmission concludes, effectively storing the complete payload in memory. When the configuration option auto_decompress is set to true, the system attempts to inflate the buffered content using zlib functions such as gunzip or inflate. Because these compression libraries return the fully decompressed output at once, a small compressed file can expand into a massive data structure that consumes substantial RAM. This behavior enables an attacker hosting a malicious server to trigger memory exhaustion simply by responding with a large payload or one designed for high expansion ratios, leading to process crashes or denial of service conditions within the Erlang runtime environment.
From a security framework perspective, this vulnerability aligns with ATT&CK techniques related to resource consumption and availability impact. The lack of input validation regarding content length headers further exacerbates the risk, as clients may trust server-provided metrics without verifying actual data volume against system constraints. This oversight permits remote attackers to execute denial-of-service attacks by manipulating network resources through standard HTTP interactions. Since any server contacted by the client can exploit this flaw, the attack surface is broad and difficult to mitigate solely through application logic changes unless explicit limits are enforced at the library level.
To address this issue, developers must upgrade to Hackney version 4.9.0 or later, where these resource management flaws have been remediated. In versions prior to 2.0.0-beta.1 up until but not including 4.9.0, the vulnerability remains present and exploitable. Mitigation strategies also include implementing application-level checks on Content-Length headers before initiating body retrieval, although this is less reliable than fixing the underlying library behavior. Additionally, configuring auto_decompress to false may reduce risk by deferring decompression until after size validation occurs at a higher layer of the application stack. Organizations relying on Hackney for HTTP communications should prioritize patching immediately to prevent potential service disruptions caused by memory exhaustion attacks originating from untrusted or compromised upstream servers.