LibreSSL

LibreSSL

Developer(s)	The OpenBSD Project
Stable release	2.1.6 (March 19, 2015 (2015-03-19)[1]) [±]
Written in	C, assembly
Operating system	OpenBSD, FreeBSD, NetBSD, Linux, HP-UX, Solaris, Mac OS X, Windows and others[2]
Type	Security library
License	Apache License 1.0, 4-clause BSD License, ISC License, and some are public domain
Website	http://www.libressl.org

LibreSSL is an open-source implementation of the Secure Sockets Layer (SSL) and Transport Layer Security (TLS) protocols. It was forked from the OpenSSL cryptographic software library in April 2014 as a response by OpenBSD developers to the Heartbleed security vulnerability in OpenSSL,^{[3][4][5][6][7]} with the aim of refactoring the OpenSSL code so as to provide a more secure implementation.^[8]

LibreSSL was forked from the OpenSSL library starting with the 1.0.1g branch and will follow the security guidelines used elsewhere in the OpenBSD project.^[9]

History

After the Heartbleed bug in OpenSSL, the OpenBSD team audited the code afresh, and quickly realised they would need to maintain a fork themselves.^[3] The libressl.org domain was registered on 11 April, 2014; the project announced the name on 22 April, 2014.

In the first week of code pruning, more than 90,000 lines of C code were removed.^[8][10] Older or unused code has been removed, and support for some older or now-rare operating systems removed. LibreSSL is initially being developed as an intended replacement for OpenSSL in OpenBSD 5.6, and it is then expected to be ported back to other platforms once a stripped-down version of the library is stable.^[11][12] As of April 2014, the project was seeking a "stable commitment" of external funding.^[10]

On 5 June 2014, several OpenSSL bugs became public. While several projects were notified in advance,^[13] LibreSSL was not; Theo de Raadt accused the OpenSSL developers of intentionally withholding this information from OpenBSD and LibreSSL.^[14]

On 20 June 2014, Google created another fork of OpenSSL called BoringSSL, and promised to exchange fixes with LibreSSL.^[15][16] Google has already relicensed some of its contributions under the ISC license, as it was requested by the LibreSSL developers.^[15][17] On 21 June, Theo de Raadt welcomed BoringSSL and outlined the plans for LibreSSL-portable.^[18] Starting on 8 July, code porting for OS X and Solaris began,^[19] while initial porting to Linux began on 20 June.^[20]

On 11 July 2014, the first portable version of LibreSSL was released as version 2.0.0.^[21][22] The first release was quickly followed by 2.0.1^[23] on 13 July, 2.0.2^[24] on 16 July, 2.0.3^[25] on 22 July, 2.0.4^[26] on 3 Aug and 2.0.5^[27] on 5 August 2014. Many issues with the first portable release were fixed in the 2.0 series.

With version 2.1.0^[28] released on 12 October 2014 the rate of change in LibreSSL became considerably lower and LibreSSL became a usable alternative to OpenSSL. Most of the changes in the 2.1 versions were related to security vulnerabilities found in OpenSSL

Changes

Memory-related

In more detail, some of the more notable and important changes thus far include replacement of custom memory calls to ones in a standard library (for example, strlcpy, calloc, asprintf, reallocarray, etc.).^[29][30] This process may help later on to catch buffer overflow errors with more advanced memory analysis tools or by simply observing program crashes (via ASLR, use of the NX bit, stack canaries, etc.).

Fixes for potential double free scenarios have also been cited in the CVS commit logs (including explicit assignments of NULL pointer values).^[31] There have been extra sanity checks also cited in the commit logs related to ensuring length arguments, unsigned-to-signed variable assignments, pointer values, and method returns.

Proactive measures

In order to maintain good programming practice, a number of compiler options and flags designed for safety have been enabled by default to help in spotting potential issues so they can be fixed earlier (-Wall, -Werror, -Wextra, -Wuninitialized). There have also been code readability updates which help future contributors in verifying program correctness (KNF, white-space, line-wrapping, etc.). Modification or removal of unneeded method wrappers and macros also help with code readability and auditing (Error and I/O abstraction library references).

Changes were made to ensure that LibreSSL will be year 2038 compatible along with maintaining portability for other similar platforms. In addition, explicit_bzero and bn_clear calls were added to prevent the compiler from optimizing them out and prevent attackers from reading previously allocated memory.

Cryptographic

There were changes to help ensure proper seeding of random number generator-based methods via replacements of insecure seeding practices (taking advantage of features offered by the kernel itself natively).^[32][33] In terms of notable additions made, OpenBSD has added support for newer and more reputable algorithms (ChaCha stream cipher and Poly1305 message authentication code) along with a safer set of elliptic curves (brainpool curves from RFC 5639, up to 512 bits in strength).

Added features

The initial release of LibreSSL added a number of features: the ChaCha and Poly1305 algorithm, the Brainpool and ANSSI elliptic curves, and the AES-GCM and ChaCha20-Poly1305 AEAD modes.

Later versions added the following:^[34]

• 2.1.0:^[28] Automatic ephemeral EC keys
• 2.1.2:^[35] Built-in arc4random implementation on OS X and FreeBSD
• 2.1.2: Reworked GOST cipher suite support
• 2.1.3:^[36] ALPN support
• 2.1.3: SHA256 Camellia cipher suites
• 2.1.4:^[37] TLS_FALLBACK_SCSV server-side support
• 2.1.4: certhash as a replacement of the c_rehash script
• 2.1.4: X509_STORE_load_mem API for loading certificates from memory (enhance chroot support)
• 2.1.4: Experimental Windows binaries
• 2.1.5:^[38] Minor update mainly for improving Windows support, first working 32- and 64-bit binaries
• 2.1.6:^[39] libtls declared stable and enabled by default

Old insecure features

The initial release of LibreSSL disabled a number of features by default.^[40] Some of the code for these features was later removed, including Kerberos, US-Export ciphers, TLS compression, DTLS heartbeat, and SSL v2.

Later versions disabled more features:

• 2.1.1:^[41] Following the discovery of the POODLE vulnerability in the legacy SSL 3.0 protocol, LibreSSL now disables the use of SSL 3.0 by default.
• 2.1.3:^[36] GOST R 34.10-94 signature authentication^[34]

Code removal

On 18 April 2014 Bob Beck reports^[42] to have removed 82000 lines of C code and 140000 lines in total from the OpenSSL 1.0.1g code.
The initial release of LibreSSL has removed a number of features that were deemed insecure, unnecessary or deprecated as part of OpenBSD 5.6^[40]

• In response to Heartbleed, the heartbeat functionality^[43] was the one of the first features to be removed
• Unneeded platforms (Classic Mac OS, NetWare, OS/2, VMS, 16-bit Windows, etc.)
• Support for old compilers
• The IBM 4758, Broadcom ubsec, Sureware, Nuron, GOST, GMP, CSwift, CHIL, CAPI, Atalla and AEP engines were removed due to irrelevance of hardware or dependency on non-free libraries
• The OpenSSL PRNG was removed (and replaced with arc4random)
• Preprocessor macros that have been deemed unnecessary or insecure or were already deprecated in OpenSSL for a long time (e.g. des_old.h)
• Older unneeded files for assembly language, C, and Perl (e.g. EGD)
• MD2, SEED functionality

The Dual_EC_DRBG algorithm, which is suspected of having a back door,^[44] was cut along with support for the FIPS 140-2 standard that required it. Unused protocols and insecure algorithms have also been removed, including the support for FIPS 140-2,^[45] MD4/MD5^[34] J-PAKE,^[40] and SRP.^[26]

Bug backlog

One of the complaints of OpenSSL was the number of open bugs reported in the bug tracker that had gone unfixed for years. Older bugs are now being fixed in LibreSSL.^[46]

Security and vulnerabilities

LibreSSL has proven not to be vulnerable to many of the issues discovered after it was forked from the OpenSSL project. Notably, none of the vulnerabilities rated "High" were applicable to LibreSSL.

Severity	LibreSSL	OpenSSL
High	0	4
Medium	12	22
Low	7	9
Total	19	35

13 July 2014

Shortly after the first portable release, LibreSSL's PRNG was found to not always reseed the PRNG when forking new processes, and to have low entropy for the seed when /dev/urandom was not available as might happen in a chroot jail.^[47] LibreSSL refers to this as the 'Linux forking and PID wrap issue'.

This was fixed in LibreSSL 2.0.2^[24]

This vulnerability does not apply to OpenSSL and is a result of the refactoring of the PRNG code in LibreSSL.

CVE reference	Description	Severity	Comment
-	Linux forking and PID wrap issue	low[note 1]

6 August 2014

OpenSSL published 9 vulnerabilities^[48]

CVE reference	Description	Severity	Comment
CVE-2014-3510	Flaw handling DTLS anonymous EC(DH) ciphersuites	medium
CVE-2014-3508	Information leak in pretty printing functions	medium	partially vulnerable
CVE-2014-3509	Race condition in ssl_parse_serverhello_tlsext	medium
CVE-2014-3505	Double Free when processing DTLS packets	medium
CVE-2014-3506	DTLS memory exhaustion	medium
CVE-2014-3507	DTLS memory leak from zero-length fragments	medium
CVE-2014-3511	OpenSSL TLS protocol downgrade attack	medium
CVE-2014-5139	Crash with SRP ciphersuite in Server Hello message	medium	Not vulnerable
CVE-2014-3512	SRP buffer overrun	high	Not vulnerable

Severity taken from the NIST National Vulnerability Database

15 October 2014

OpenSSL responds to the POODLE attack and publishes 4 vulnerabilities^[49]

NB: As of this advisory, OpenSSL includes severity ratings to vulnerabilities

CVE reference	Description	Severity	Comment
	SSL 3.0 Fallback protection	medium	LibreSSL disables SSLv3 [50] Adds TLS_SCSV_FALLBACK in 2.1.4
CVE-2014-3568	Build option no-ssl3 is incomplete	low
CVE-2014-3513	SRTP Memory Leak	high	Not vulnerable
CVE-2014-3567	Session Ticket Memory Leak	medium	Not vulnerable

8 January 2015

OpenSSL publishes 8 vulnerabilities^[51] discovered by the OpenSSL code review.

CVE reference	Description	Severity	Comment
CVE-2014-8275	Certificate fingerprints can be modified	low	Fixed in 2.1.4
CVE-2014-3572	ECDHE silently downgrades to ECDH [Client]	low	Fixed in 2.1.4
CVE-2014-3570	Bignum squaring may produce incorrect results	low	Fixed in 2.1.4
CVE-2015-0205	DH client certificates accepted without verification [Server]	low	Fixed in 2.1.4
CVE-2015-0206	DTLS memory leak in dtls1_buffer_record	moderate	Fixed in earlier release
CVE-2014-3571	DTLS segmentation fault in dtls1_get_record	moderate	Not vulnerable
CVE-2014-3569	no-ssl3 configuration sets method to NULL	low	Not vulnerable
CVE-2015-0204	RSA silently downgrades to EXPORT_RSA [Client]	low	Not vulnerable

19 March 2015

OpenSSL publishes 14 vulnerabilities^[52] discovered by the OpenSSL code review. LibreSSL confirms that 5 of these vulnerabilities apply to LibreSSL as well.^[53] notably not CVE-2015-0291 which has the highest possible impact rating for OpenSSL. LibreSSL released 2.1.6^[39] to fix these security issues.

CVE reference	Description	Severity	Comment
CVE-2015-0286	Segmentation fault in ASN1_TYPE_cmp	moderate	Fixed in 2.1.6
CVE-2015-0287	ASN.1 structure reuse memory corruption	moderate	Fixed in 2.1.6
CVE-2015-0288	X509_to_X509_REQ NULL pointer deref	moderate	Fixed in 2.1.6
CVE-2015-0289	PKCS7 NULL pointer dereferences	moderate	Fixed in 2.1.6
CVE-2015-0209	Use After Free following d2i_ECPrivatekey error	low	Fixed in 2.1.6
CVE-2015-0291	ClientHello sigalgs DoS	high	Affected code is not present
CVE-2015-0204	RSA silently downgrades to EXPORT_RSA [Client]	high	Fixed in LibreSSL 2.1.2 - reclassifed from low to high
CVE-2015-0207	Segmentation fault in DTLSv1_listen	moderate	LibreSSL is not vulnerable, but the fix was safe to merge
CVE-2015-0208	Segmentation fault for invalid PSS parameters	moderate	Affected code is not present
CVE-2015-0290	Multiblock corrupted pointer	moderate	Affected code is not present
CVE-2015-0292	Base64 decode	moderate	Fixed in LibreSSL 2.0.0
CVE-2015-0293	DoS via reachable assert in SSLv2 servers	moderate	Affected code is not present
CVE-2015-0285	Handshake with unseeded PRNG	low	Cannot happen by the design of the LibreSSL PRNG
CVE-2015-1787	Empty CKE with client auth and DHE	moderate	Fixed in LibreSSL 2.0.1

See also

• Comparison of TLS implementations
• OpenSSH
• POSSE project

References

External links

• Official website
• LibreSSL source code (OpenGrok)
• OpenSSL Valhalla Rampage (blog of highlights of the code cleanup)
• LibreSSL status on FreeBSD
• LibreSSL ebuilds testing repo on Gentoo

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