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curl FTP path confusion leads to NIL byte out of bounds write

Critical severity GitHub Reviewed Published May 14, 2022 to the GitHub Advisory Database • Updated Mar 1, 2023

Package

nuget curl (NuGet)

Affected versions

>= 7.12.3, < 7.59.0

Patched versions

None

Description

curl can be coerced into writing a zero byte out of bounds.

This bug can trigger when curl is told to work on an FTP URL, with the setting to only issue a single CWD command (--ftp-method singlecwd or the libcurl alternative CURLOPT_FTP_FILEMETHOD).

curl then URL-decodes the given path, calls strlen() on the result and deducts the length of the file name part to find the end of the directory within the buffer. It then writes a zero byte on that index, in a buffer allocated on the heap.

If the directory part of the URL contains a %00 sequence, the directory length might end up shorter than the file name path, making the calculation size_t index = directory_len - filepart_len end up with a huge index variable for where the zero byte gets stored: heap_buffer[index] = 0. On several architectures that huge index will wrap and work as a negative value, thus overwriting memory before the intended heap buffer.

By using different file part lengths and putting the string %00 in different places in the URL, an attacker that can control what paths a curl-using application uses can write that zero byte on different indexes.

References

Published by the National Vulnerability Database Mar 14, 2018
Published to the GitHub Advisory Database May 14, 2022
Reviewed Mar 1, 2023
Last updated Mar 1, 2023

Severity

Critical

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS score

0.553%
(78th percentile)

Weaknesses

CVE ID

CVE-2018-1000120

GHSA ID

GHSA-674j-7m97-j2p9

Source code

Credits

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