CVE-2021-20305

NameCVE-2021-20305
DescriptionA flaw was found in Nettle in versions before 3.7.2, where several Nettle signature verification functions (GOST DSA, EDDSA & ECDSA) result in the Elliptic Curve Cryptography point (ECC) multiply function being called with out-of-range scalers, possibly resulting in incorrect results. This flaw allows an attacker to force an invalid signature, causing an assertion failure or possible validation. The highest threat to this vulnerability is to confidentiality, integrity, as well as system availability.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub code/issues, web search, more)
NVD severitymedium
Debian Bugs985652

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
nettle (PTS)stretch3.3-1vulnerable
buster3.4.1-1vulnerable
bullseye, sid3.7.2-3fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
nettlesource(unstable)3.7.2-1985652

Notes

[buster] - nettle <no-dsa> (Minor issue)
[stretch] - nettle <postponed> (Minor issue; can be fixed in next update)
https://lists.lysator.liu.se/pipermail/nettle-bugs/2021/009457.html
New functions ecc_mod_mul_canonical and ecc_mod_sqr_canonical:
https://git.lysator.liu.se/nettle/nettle/-/commit/a63893791280d441c713293491da97c79c0950fe
Use ecc_mod_mul_canonical for point comparison:
https://git.lysator.liu.se/nettle/nettle/-/commit/971bed6ab4b27014eb23085e8176917e1a096fd5
Fix bug in ecc_ecdsa_verify:
https://git.lysator.liu.se/nettle/nettle/-/commit/74ee0e82b6891e090f20723750faeb19064e31b2
Ensure ecdsa_sign output is canonically reduced:
https://git.lysator.liu.se/nettle/nettle/-/commit/51f643eee00e2caa65c8a2f5857f49acdf3ef1ce
Analogous fix to ecc_gostdsa_verify:
https://git.lysator.liu.se/nettle/nettle/-/commit/401c8d53d8a8cf1e79980e62bda3f946f8e07c14
Similar fix for eddsa:
https://git.lysator.liu.se/nettle/nettle/-/commit/ae3801a0e5cce276c270973214385c86048d5f7b
Fix canonical reduction in gostdsa_vko:
https://git.lysator.liu.se/nettle/nettle/-/commit/63f222c60b03470c0005aa9bc4296fbf585f68b9

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