curl / Development / Vulnerability Disclosure Policy

curl vulnerability disclosure policy

This document describes how security vulnerabilities are handled in the curl project.

Publishing Information

All known and public curl or libcurl related vulnerabilities are listed on the curl website security page.

Security vulnerabilities should not be entered in the project's public bug tracker.

Vulnerability Handling

The typical process for handling a new security vulnerability is as follows.

No information should be made public about a vulnerability until it is formally announced at the end of this process. That means, for example, that a bug tracker entry must NOT be created to track the issue since that makes the issue public and it should not be discussed on any of the project's public mailing lists. Messages associated with any commits should not make any reference to the security nature of the commit if done prior to the public announcement.

security (at curl dot se)

This is a private mailing list for discussions on and about curl security issues.

Who is on this list? There are a couple of criteria you must meet, and then we might ask you to join the list or you can ask to join it. It really is not a formal process. We basically only require that you have a long-term presence in the curl project and you have shown an understanding for the project and its way of working. You must have been around for a good while and you should have no plans of vanishing in the near future.

We do not make the list of participants public mostly because it tends to vary somewhat over time and a list somewhere only risks getting outdated.

Publishing Security Advisories

  1. Write up the security advisory, using markdown syntax. Use the same subtitles as last time to maintain consistency.

  2. Name the advisory file after the allocated CVE id.

  3. Add a line on the top of the array in curl-www/docs/

  4. Put the new advisory markdown file in the curl-www/docs/ directory. Add it to the git repository.

  5. Run make in your local web checkout and verify that things look fine.

  6. On security advisory release day, push the changes on the curl-www repository's remote master branch.


Request the issue to be disclosed. If there are sensitive details present in the report and discussion, those should be redacted from the disclosure. The default policy is to disclose as much as possible as soon as the vulnerability has been published.

Bug Bounty

See BUG-BOUNTY for details on the bug bounty program.

Severity levels

The curl project's security team rates security problems using four severity levels depending how serious we consider the problem to be. We use Low, Medium, High and Critical. We refrain from using numerical scoring of vulnerabilities.

When deciding severity level on a particular issue, we take all the factors into account: attack vector, attack complexity, required privileges, necessary build configuration, protocols involved, platform specifics and also what effects a possible exploit or trigger of the issue can lead do, including confidentiality, integrity or availability problems.


This is a security problem that is truly hard or unlikely to exploit or trigger. Due to timing, platform requirements or the fact that options or protocols involved are rare etc. Past example


This is a security problem that is less hard than Low to exploit or trigger. Less strict timing, wider platforms availability or involving more widely used options or protocols. A problem that usually needs something else to also happen to become serious. Past example


This issue in itself a serious problem with real world impact. Flaws that can easily compromise the confidentiality, integrity or availability of resources. Exploiting or triggering this problem is not hard. Past example


Easily exploitable by a remote unauthenticated attacker and lead to system compromise (arbitrary code execution) without requiring user interaction, with a common configuration on a popular platform. This issue has few restrictions and requirements and can be exploited easily using most curl configurations. Past example

Not security issues

This is an incomplete list of issues that are not considered vulnerabilities.

Small memory leaks

We do not consider a small memory leak a security problem; even if the amount of allocated memory grows by a small amount every now and then. Long-living applications and services already need to have counter-measures and deal with growing memory usage, be it leaks or just increased use. A small memory or resource leak is then expected to not cause a security problem.

Of course there can be a discussion if a leak is small or not. A large leak can be considered a security problem due to the DOS risk. If leaked memory contains sensitive data it might also qualify as a security problem.

Never-ending transfers

We do not consider flaws that cause a transfer to never end to be a security problem. There are already several benign and likely reasons for transfers to stall and never end, so applications that cannot deal with never-ending transfers already need to have counter-measures established.

If the problem avoids the regular counter-measures when it causes a never- ending transfer, it might be a security problem.

Not practically possible

If the flaw or vulnerability cannot practically get executed on existing hardware it is not a security problem.

API misuse

If a reported issue only triggers by an application using the API in a way that is not documented to work or even documented to not work, it is probably not going to be considered a security problem. We only guarantee secure and proper functionality when the APIs are used as expected and documented.

There can be a discussion about what the documentation actually means and how to interpret the text, which might end up with us still agreeing that it is a security problem.

Local attackers already present

When an issue can only be attacked or misused by an attacker present on the local system or network, the bar is raised. If a local user wrongfully has elevated rights on your system enough to attack curl, they can probably already do much worse harm and the problem is not really in curl.


Vulnerabilities in features which are off by default (in the build) and documented as experimental, are not eligible for a reward and we do not consider them security problems.

URL inconsistencies

URL parser inconsistencies between browsers and curl are expected and are not considered security vulnerabilities. The WHATWG URL Specification and RFC 3986+ (the plus meaning that it is an extended version) are not completely interoperable.

Obvious parser bugs can still be vulnerabilities of course.

Visible command line arguments

The curl command blanks the contents of a number of command line arguments to prevent them from appearing in process listings. It does not blank all arguments even if some of them that are not blanked might contain sensitive data. We consider this functionality a best-effort and omissions are not security vulnerabilities.


Busy-loops that consume 100% CPU time but eventually end (perhaps due to a set timeout value or otherwise) are not considered security problems. Applications are supposed to already handle situations when the transfer loop legitimately consumes 100% CPU time, so while a prolonged such busy-loop is a nasty bug, we do not consider it a security problem.

Saving files

curl cannot protect against attacks where an attacker has write access to the same directory where curl is directed to save files.

Tricking a user to run a command line

A creative, misleading or funny looking command line is not a security problem. The curl command line tool takes options and URLs on the command line and if an attacker can trick the user to run a specifically crafted curl command line, all bets are off. Such an attacker can just as well have the user run a much worse command that can do something fatal (like sudo rm -rf /).

Terminal output and escape sequences

Content that is transferred from a server and gets displayed in a terminal by curl may contain escape sequences or use other tricks to fool the user. This is curl working as designed and is not a curl security problem. Escape sequences, moving cursor, changing color etc, is also frequently used for good. To reduce the risk of getting fooled, save files and browse them after download using a display method that minimizes risks.