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Date: Wed, 15 Feb 2023 08:28:58 +0100 (CET)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,, libcurl hacking <>,
Subject: curl: CVE-2023-23916: HTTP multi-header compression denial of

CVE-2023-23916: HTTP multi-header compression denial of service

Project curl Security Advisory, February 15th 2023 -


curl supports "chained" HTTP compression algorithms, meaning that a server
response can be compressed multiple times and potentially with different
algorithms. The number of acceptable "links" in this "decompression chain" was
capped, but the cap was implemented on a per-header basis allowing a malicious
server to insert a virtually unlimited number of compression steps simply by
using many headers.

The use of such a decompression chain could result in a "malloc bomb", making
curl end up spending enormous amounts of allocated heap memory, or trying to
and returning out of memory errors.

We are not aware of any exploit of this flaw.


CVE-2023-23916 was introduced in [commit
shipped in curl 7.57.0.

Automatic decompression of content needs to be enabled per transfer. It is
disabled by default and then nothing bad happens.

This flaw exists with one or more of the compression algorithms built-in
(gzip, brotli or zstd), but the individual algorithms have different
"exploding" powers.

Both `Content-Encoding:` and `Transfer-Encoding:` are affected over all HTTP

This flaw is almost identical to the previous [CVE-2022-32206: HTTP
compression denial of service](, as
the fix for that earlier flaw was incomplete.

CWE-770: Allocation of Resources Without Limits or Throttling

Severity: Medium


- Affected versions: curl 7.57.0 to and including 7.87.0
- Not affected versions: curl < 7.57.0 and curl >= 7.87.0

libcurl is used by many applications, but not always advertised as such!


The amount of accepted "chained" algorithms is now capped to 5 in total,
independently of the number of headers.

A [fix for CVE-2023-23916](


  A - Upgrade curl to version 7.88.0

  B - Apply the patch to your local version

  C - Do not enable automatic decompression


This issue was reported to the curl project on January 8, 2023. We contacted
distros@...nwall on February 7, 2023.

libcurl 7.88.0 was released on February 15 2023, coordinated with the
publication of this advisory.


- Reported-by: Patrick Monnerat
- Patched-by: Patrick Monnerat

Thanks a lot!


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