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CVE-2025-53020 is a denial-of-service vulnerability in Apache HTTP Server's HTTP/2 handling, affecting versions 2.4.17 through 2.4.63. The flaw is described as a late release of memory after effective lifetime and is triggered when a client sends repeated request header names over an HTTP/2 connection. This causes the server to retain or over-allocate memory associated with header processing longer than intended, allowing memory consumption on a connection to grow disproportionately. The issue is associated with Apache's HTTP/2 implementation and was fixed in Apache HTTP Server 2.4.64.
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What an attacker gets, and what they’ve been doing with it.
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Patch, then assume compromise.
1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
This repository contains a proof-of-concept (PoC) exploit for CVE-2025-53020, a memory exhaustion vulnerability in Apache httpd's HTTP/2 implementation. The repository consists of two files: a detailed README.md explaining the vulnerability, attack mechanism, and usage instructions, and poc.py, a Python script that implements the exploit logic. The exploit abuses the HPACK header compression in HTTP/2 by sending requests with repeated long header names, causing the server to allocate excessive memory for each repetition. The script allows customization of header length, number of repetitions, batch size, and delay between batches. It supports both HTTP and HTTPS targets and includes a patch for the h2 library to handle empty header values correctly. The primary attack vector is network-based, targeting HTTP/2 endpoints on Apache httpd servers. The exploit is a functional PoC and does not include weaponized payloads beyond denial of service. No hardcoded IPs or domains are present; endpoints are user-supplied via command-line arguments. The repository is intended for authorized security testing and research.
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Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
16 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An Apache HTTPD vulnerability related to the HPACK Bomb technique, addressed in Apache version 2.4.64.
A memory exhaustion vulnerability in Apache httpd's HTTP/2 implementation.
A prior Apache httpd vulnerability involving roughly 4,000:1 memory amplification related to HTTP/2 handling.
An Apache httpd vulnerability involving strong HPACK-based amplification, cited as a precursor to the newly described attack chain.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.