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ADD: MuPDF v1.26.7: the MuPDF source as downloaded by a default build of PyMuPDF 1.26.4. The directory name has changed: no version number in the expanded directory now.
author Franz Glasner <fzglas.hg@dom66.de>
date Mon, 15 Sep 2025 11:43:07 +0200
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1 License Mixing
2 ==============
3
4 libcurl can be built to use a fair amount of various third party libraries,
5 libraries that are written and provided by other parties that are distributed
6 using their own licenses. Even libcurl itself contains code that may cause
7 problems to some. This document attempts to describe what licenses libcurl and
8 the other libraries use and what possible dilemmas linking and mixing them all
9 can lead to for end users.
10
11 I am not a lawyer and this is not legal advice!
12
13 One common dilemma is that [GPL](https://www.gnu.org/licenses/gpl.html)
14 licensed code is not allowed to be linked with code licensed under the
15 [Original BSD license](https://spdx.org/licenses/BSD-4-Clause.html) (with the
16 announcement clause). You may still build your own copies that use them all,
17 but distributing them as binaries would be to violate the GPL license - unless
18 you accompany your license with an
19 [exception](https://www.gnu.org/licenses/gpl-faq.html#GPLIncompatibleLibs). This
20 particular problem was addressed when the [Modified BSD
21 license](https://opensource.org/licenses/BSD-3-Clause) was created, which does
22 not have the announcement clause that collides with GPL.
23
24 ## libcurl
25
26 Uses an [MIT style license](https://curl.haxx.se/docs/copyright.html) that is
27 very liberal.
28
29 ## OpenSSL
30
31 (May be used for SSL/TLS support) Uses an Original BSD-style license with an
32 announcement clause that makes it "incompatible" with GPL. You are not
33 allowed to ship binaries that link with OpenSSL that includes GPL code
34 (unless that specific GPL code includes an exception for OpenSSL - a habit
35 that is growing more and more common). If OpenSSL's licensing is a problem
36 for you, consider using another TLS library.
37
38 ## GnuTLS
39
40 (May be used for SSL/TLS support) Uses the
41 [LGPL](https://www.gnu.org/licenses/lgpl.html) license. If this is a problem
42 for you, consider using another TLS library. Also note that GnuTLS itself
43 depends on and uses other libs (libgcrypt and libgpg-error) and they too are
44 LGPL- or GPL-licensed.
45
46 ## WolfSSL
47
48 (May be used for SSL/TLS support) Uses the GPL license or a proprietary
49 license. If this is a problem for you, consider using another TLS library.
50
51 ## NSS
52
53 (May be used for SSL/TLS support) Is covered by the
54 [MPL](https://www.mozilla.org/MPL/) license, the GPL license and the LGPL
55 license. You may choose to license the code under MPL terms, GPL terms, or
56 LGPL terms. These licenses grant you different permissions and impose
57 different obligations. You should select the license that best meets your
58 needs.
59
60 ## mbedTLS
61
62 (May be used for SSL/TLS support) Uses the [Apache 2.0
63 license](https://opensource.org/licenses/Apache-2.0) or the GPL license.
64 You may choose to license the code under Apache 2.0 terms or GPL terms.
65 These licenses grant you different permissions and impose different
66 obligations. You should select the license that best meets your needs.
67
68 ## BoringSSL
69
70 (May be used for SSL/TLS support) As an OpenSSL fork, it has the same
71 license as that.
72
73 ## libressl
74
75 (May be used for SSL/TLS support) As an OpenSSL fork, it has the same
76 license as that.
77
78 ## c-ares
79
80 (Used for asynchronous name resolves) Uses an MIT license that is very
81 liberal and imposes no restrictions on any other library or part you may link
82 with.
83
84 ## zlib
85
86 (Used for compressed Transfer-Encoding support) Uses an MIT-style license
87 that shouldn't collide with any other library.
88
89 ## MIT Kerberos
90
91 (May be used for GSS support) MIT licensed, that shouldn't collide with any
92 other parts.
93
94 ## Heimdal
95
96 (May be used for GSS support) Heimdal is Original BSD licensed with the
97 announcement clause.
98
99 ## GNU GSS
100
101 (May be used for GSS support) GNU GSS is GPL licensed. Note that you may not
102 distribute binary curl packages that uses this if you build curl to also link
103 and use any Original BSD licensed libraries!
104
105 ## libidn
106
107 (Used for IDNA support) Uses the GNU Lesser General Public License [3]. LGPL
108 is a variation of GPL with slightly less aggressive "copyleft". This license
109 requires more requirements to be met when distributing binaries, see the
110 license for details. Also note that if you distribute a binary that includes
111 this library, you must also include the full LGPL license text. Please
112 properly point out what parts of the distributed package that the license
113 addresses.
114
115 ## OpenLDAP
116
117 (Used for LDAP support) Uses a Modified BSD-style license. Since libcurl uses
118 OpenLDAP as a shared library only, I have not heard of anyone that ships
119 OpenLDAP linked with libcurl in an app.
120
121 ## libssh2
122
123 (Used for scp and sftp support) libssh2 uses a Modified BSD-style license.