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GHSA-jcvh-xf52-2cwm
github.com/ffuf/ffufgithub.com/ffuf/ffuf/v2Summary
A malicious or attacker-controlled target server can crash ffuf with an out-of-memory condition by returning a compressed HTTP response that decompresses to a very large body (a decompression bomb). This works against default usage with no special flags.
Details
The response body size guard in pkg/runner/simple.go only checks the server-supplied Content-Length header, which reflects the compressed size and is absent for chunked responses or when Go's
net/http transport transparently decompresses the body. After that check, io.ReadAll reads the entire decompressed stream into memory with no upper bound, so a small compressed body that
expands to gigabytes causes unbounded allocation and the process is terminated by the OS OOM killer.
The guard is bypassed in three independent ways:
- gzip (default configuration): the transport requests gzip on its own and transparently decompresses the response, stripping
Content-EncodingandContent-Length, so the size check is skipped and the already-decoded body is read unbounded. - brotli/deflate (or gzip with headers preserved):
Content-Lengthreflects the small compressed size and passes the check; the body is then manually decompressed into an unboundedio.ReadAll. - chunked transfer encoding: no
Content-Lengthheader is present, so the numeric parse fails and the check is skipped entirely.
Impact
Denial of service against the operator running ffuf. A single hostile endpoint can OOM-kill ffuf on a default invocation such as ffuf -u http://target/FUZZ -w wordlist.txt, discarding all
in-memory scan results. Because the crash recurs on every attempt against that target, a server can effectively make itself immune to ffuf-based content discovery. There is no confidentiality or
integrity impact; only the availability of the scanning process is affected. CVSS 3.1 base score 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H), CWE-409 (Improper Handling of Highly Compressed Data).
Patches
Fixed in ffuf 2.2.0 (https://github.com/ffuf/ffuf/releases/tag/v2.2.0) via https://github.com/ffuf/ffuf/pull/897. The response body read is now bounded with io.LimitReader to the existing 5
MB download cap regardless of Content-Encoding, chunked framing, or transport-level decompression; responses exceeding the cap are dropped rather than read into memory. Upgrade to 2.2.0 or later.
Workarounds
There is no configuration flag that fully mitigates this in affected versions. Until upgrading, limit ffuf usage against untrusted or attacker-influenced targets. Upgrading to 2.2.0 is the fix.
Credits
Reported by João Tricta (Hakai Offensive Security).
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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