Debian LTS: Security Advisory for curl (DLA-2500-1)

Published: 2020-12-19 04:00:25
CVE Author: NIST National Vulnerability Database

CVSS Base Vector:
AV:N/AC:L/Au:N/C:N/I:N/A:P

Summary:
The remote host is missing an update for the 'curl' Linux Distribution Package(s) announced via the DLA-2500-1 advisory.

Detection Method:
Checks if a vulnerable Linux Distribution Package version is present on the target host.

Technical Details:
Several vulnerabilities were discovered in curl, a command line tool for transferring data with URL syntax and an easy-to-use client-side URL transfer library. CVE-2020-8284 When curl performs a passive FTP transfer, it first tries the EPSV command and if that is not supported, it falls back to using PASV. Passive mode is what curl uses by default. A server response to a PASV command includes the (IPv4) address and port number for the client to connect back to in order to perform the actual data transfer. This is how the FTP protocol is designed to work. A malicious server can use the PASV response to trick curl into connecting back to a given IP address and port, and this way potentially make curl extract information about services that are otherwise private and not disclosed, for example doing port scanning and service banner extractions. The IP address part of the response is now ignored by default, by making CURLOPT_FTP_SKIP_PASV_IP default to 1L instead of previously being 0L. This has the minor drawback that a small fraction of use cases might break, when a server truly needs the client to connect back to a different IP address than what the control connection uses and for those CURLOPT_FTP_SKIP_PASV_IP can be set to 0L. The same goes for the command line tool, which then might need --no-ftp-skip-pasv-ip set to prevent curl from ignoring the address in the server response. CVE-2020-8285 libcurl offers a wildcard matching functionality, which allows a callback (set with CURLOPT_CHUNK_BGN_FUNCTION) to return information back to libcurl on how to handle a specific entry in a directory when libcurl iterates over a list of all available entries. When this callback returns CURL_CHUNK_BGN_FUNC_SKIP, to tell libcurl to not deal with that file, the internal function in libcurl then calls itself recursively to handle the next directory entry. If there's a sufficient amount of file entries and if the callback returns 'skip' enough number of times, libcurl runs out of stack space. The exact amount will of course vary with platforms, compilers and other environmental factors. The content of the remote directory is not kept on the stack, so it seems hard for the attacker to control exactly what data that overwrites the stack - however it remains a Denial-Of-Service vector as a malicious user who controls a server that a libcurl-using application works with under these premises can trigger a crash. The internal function is rewritten to instead and more appropriately use an ordinary loop instead of the recursive approach. This way, the stack use will remain the same no matter how many files that are skipped. CVE-202 ... Description truncated. Please see the references for more information.

Affected Versions:
'curl' Linux Distribution Package(s) on Debian Linux.

Recommendations:
For Debian 9 stretch, these problems have been fixed in version 7.52.1-5+deb9u13. We recommend that you upgrade your curl Linux Distribution Packages.

Solution Type:
Vendor Patch

Detection Type:
Linux Distribution Package

NIST (National Institute of Standards and Technology) NVD (National Vulnerability Database)

https://nvd.nist.gov/vuln/detail/CVE-2020-8284
https://nvd.nist.gov/vuln/detail/CVE-2020-8285
https://nvd.nist.gov/vuln/detail/CVE-2020-8286

References:

https://lists.debian.org/debian-lts-announce/2020/12/msg00029.html
https://security-tracker.debian.org/tracker/DLA-2500-1
https://bugs.debian.org/977161
https://bugs.debian.org/977162
https://bugs.debian.org/977163

Severity
Medium
CVSS Score
5.0
Published
2020-12-19
Modified
2020-12-19
Category
Debian Local Security Checks

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