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Date: Mon, 20 Mar 2023 08:26:06 +0100 (CET)
From: Daniel Stenberg <>
To: curl security announcements -- curl users <>,, libcurl hacking <>,
Subject: [SECURITY ADVISORY] curl: CVE-2023-27534: SFTP path ~ resolving

CVE-2023-27534: SFTP path ~ resolving discrepancy

Project curl Security Advisory, March 20th 2023 -


curl supports SFTP transfers. curl's SFTP implementation offers a special
feature in the path component of URLs: a tilde (`~`) character as the first
path element in the path to denotes a path relative to the user's home
directory. This is supported because of wording in the [once proposed
to-become RFC
that was to dictate how SFTP URLs work.

Due to a bug, the handling of the tilde in SFTP path did however not only
replace it when it is used stand-alone as the first path element but also
wrongly when used as a mere prefix in the first element.

Using a path like `/~2/foo` when accessing a server using the user `dan` (with
home directory `/home/dan`) would then quite surprisingly access the file

This can be taken advantage of to circumvent filtering or worse.

We are not aware of any exploit of this flaw.


CVE-2023-27534 was introduced in [commit
ba6f20a244](, shipped in curl

CWE-22: Improper Limitation of a Pathname to a Restricted Directory

Severity: Low


- Affected versions: curl 7.18.0 to and including 7.88.1
- Not affected versions: curl < 7.18.0 and curl >= 8.0.0

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


A [fix for CVE-2023-27534](


  A - Upgrade curl to version 8.0.0

  B - Apply the patch to your local version

  C - Avoid using tilde in SFTP URL paths.


This issue was reported to the curl project on March 5, 2023. We contacted
distros@...nwall on March 13, 2023.

curl 8.0.0 was released on March 20 2023, coordinated with the publication of
this advisory.


- Reported-by: Harry Sintonen
- Patched-by: Daniel Stenberg

Thanks a lot!


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