We’re publishing HTTP/2 Bomb, a remote denial-of-service exploit against most major web servers, including:

nginx

Apache httpd

Microsoft IIS

Envoy

Cloudflare Pingora

The vulnerable behavior exists in each server's default HTTP/2 configuration.

The attack was discovered by Codex, which chained two techniques known to humans for a decade: a compression bomb and a Slowloris-style hold. The bomb targets HPACK, HTTP/2's header compression scheme: one byte on the wire becomes one full header allocation on the server, repeated thousands of times per request. The hold is a zero-byte flow-control window that keeps the server from ever freeing any of it.

A curious search on Shodan revealed 880,000+ websites supporting HTTP/2 and running one of these servers, though many sit behind a CDN, which is much harder to bring down.

A home computer on a 100Mbps connection can render a vulnerable server inaccessible within seconds. Against Apache httpd and Envoy, a single client can consume and hold 32GB of server memory in roughly 20 seconds.

Buffer overflow in the ScStoragePathFromUrl function in the WebDAV service in Internet Information Services (IIS) 6.0 in Microsoft Windows Server 2003 R2 allows remote attackers to execute arbitrary code via a long header beginning with "If: <http://" in a PROPFIND request, as exploited in the wild in July or August 2016.

The SMTP service in Microsoft Internet Information Services (IIS) 4.0 and 5.0 allows remote attackers to bypass anti-relaying rules and send spam or spoofed messages via encapsulated SMTP addresses, a similar vulnerability to CVE-1999-0682.

Microsoft Internet Information Server (IIS) 5.1 may allow remote attackers to view the contents of a Frontpage Server Extension (FPSE) file, as claimed using an HTTP request for colegal.htm that contains .. (dot dot) sequences.

DISPUTED A certain ActiveX control in iisext.dll in Microsoft Internet Information Services (IIS) allows remote attackers to set a password via a string argument to the SetPassword method. NOTE: this issue could not be reproduced by a reliable third party. In addition, the original researcher is unreliable. Therefore the original disclosure is probably erroneous.

A certain ActiveX control in adsiis.dll in Microsoft Internet Information Services (IIS) allows remote attackers to cause a denial of service (browser crash) via a long string in the second argument to the GetObject method. NOTE: this issue was disclosed by an unreliable researcher, so it might be incorrect.

Integer overflow in the Internet Printing Protocol (IPP) ISAPI extension in Microsoft Internet Information Services (IIS) 5.0 through 7.0 on Windows 2000 SP4, XP SP2 and SP3, Server 2003 SP1 and SP2, and Server 2008 allows remote authenticated users to execute arbitrary code via an HTTP POST request that triggers an outbound IPP connection from a web server to a machine operated by the attacker, aka "Integer Overflow in IPP Service Vulnerability."

Unspecified vulnerability in Microsoft Internet Information Services (IIS) 5.0 through 7.0 allows local users to gain privileges via unknown vectors related to file change notifications in the TPRoot, NNTPFile\Root, or WWWRoot folders.

Microsoft Internet Information Services (IIS), when used in conjunction with unspecified third-party upload applications, allows remote attackers to create empty files with arbitrary extensions via a filename containing an initial extension followed by a : (colon) and a safe extension, as demonstrated by an upload of a .asp:.jpg file that results in creation of an empty .asp file, related to support for the NTFS Alternate Data Streams (ADS) filename syntax. NOTE: it could be argued that this is a vulnerability in the third-party product, not IIS, because the third-party product should be applying its extension restrictions to the portion of the filename before the colon.

Stack consumption vulnerability in the FTP Service in Microsoft Internet Information Services (IIS) 5.0 through 7.0 allows remote authenticated users to cause a denial of service (daemon crash) via a list (ls) -R command containing a wildcard that references a subdirectory, followed by a .. (dot dot), aka "IIS FTP Service DoS Vulnerability."

The WebDAV extension in Microsoft Internet Information Services (IIS) 5.1 and 6.0 allows remote attackers to bypass URI-based protection mechanisms, and list folders or read, create, or modify files, via a %c0%af (Unicode / character) at an arbitrary position in the URI, as demonstrated by inserting %c0%af into a "/protected/" initial pathname component to bypass the password protection on the protected\ folder, aka "IIS 5.1 and 6.0 WebDAV Authentication Bypass Vulnerability," a different vulnerability than CVE-2009-1122.

The WebDAV extension in Microsoft Internet Information Services (IIS) 5.0 on Windows 2000 SP4 does not properly decode URLs, which allows remote attackers to bypass authentication, and possibly read or create files, via a crafted HTTP request, aka "IIS 5.0 WebDAV Authentication Bypass Vulnerability," a different vulnerability than CVE-2009-1535.

Heap-based buffer overflow in the TELNETSTREAMCONTEXT::OnSendData function in ftpsvc.dll in Microsoft FTP Service 7.0 and 7.5 for Internet Information Services (IIS) 7.0, and IIS 7.5, allows remote attackers to execute arbitrary code or cause a denial of service (daemon crash) via a crafted FTP command, aka "IIS FTP Service Heap Buffer Overrun Vulnerability." NOTE: some of these details are obtained from third party information.

Microsoft .NET Framework 1.1 SP1, 2.0 SP1 and SP2, 3.5, 3.5 SP1, 3.5.1, and 4.0, as used for ASP.NET in Microsoft Internet Information Services (IIS), provides detailed error codes during decryption attempts, which allows remote attackers to decrypt and modify encrypted View State (aka VIEWSTATE) form data, and possibly forge cookies or read application files, via a padding oracle attack, aka "ASP.NET Padding Oracle Vulnerability."

Stack consumption vulnerability in the ASP implementation in Microsoft Internet Information Services (IIS) 5.1, 6.0, 7.0, and 7.5 allows remote attackers to cause a denial of service (daemon outage) via a crafted request, related to asp.dll, aka "IIS Repeated Parameter Request Denial of Service Vulnerability."