CVE-2026-85721 AsyncHttpClient: Unbounded HTTP/1.1 response decompression enables a decompression-bomb denial of service
A malicious server can cause a Java application using AsyncHttpClient to crash via a decompression bomb, requiring an upgrade to patched versions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-85721?
CVE-2026-85721 is a high-severity denial of service vulnerability in AsyncHttpClient async-http-client, published on 17 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
The AsyncHttpClient (AHC) library allows Java applications to easily execute HTTP requests and asynchronously process HTTP responses. From 2.0.0 until 2.16.1 and 3.0.12, automatic response decompression on the HTTP/1.1 path uses ChannelManager.newHttpContentDecompressor() to install Http1ContentDecompressor without a cumulative output-size limit. A hostile or compromised server, or an attacker who can alter a response in transit, can send a small gzip, deflate, or snappy response that expands across chunks until the client exhausts its heap and raises OutOfMemoryError; brotli and zstd are also affected when their optional codecs are present. In versions 3.0.8 through 3.0.10, the HTTP/2 decompressor is also unbounded, so switching protocols does not mitigate the issue on those releases. A limit applied to each decode call is insufficient because the response can be delivered as many small chunks, so the fixed implementation tracks total decompressed bytes for the whole response. This issue is fixed in versions 2.16.1 and 3.0.12.
Which versions are affected by CVE-2026-85721?
4 open source packages ship an affected version, including org.asynchttpclient:async-http-client.
| Package | Affected | Fixed in |
|---|---|---|
org.asynchttpclient:async-http-client Maven | From 2.0.0 | 2.16.1 |
org.asynchttpclient:async-http-client Maven | From 2.0.0 | 2.16.1 |
org.asynchttpclient:async-http-client Maven | From 3.0.0 | 3.0.12 |
org.asynchttpclient:async-http-client Maven | From 3.0.0 | 3.0.12 |
How do I fix CVE-2026-85721?
Upgrade org.asynchttpclient:async-http-client to a fixed version for your release line: 2.16.1 or 3.0.12.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-85721 being exploited?
There is no known exploitation of CVE-2026-85721 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as DEBIAN-CVE-2026-85721, ECHO-b14e-ac13-29f3, GHSA-7grg-jcf7-rpmx, MINI-j7c4-x85w-4fr3, MINI-m8hh-phpp-vffx, MINI-ppv3-254v-fffv and 3 more.