The sync endpoint in YubiKey Validation Server before 2.40 allows remote attackers to replay an OTP.

published 2020-03-05 6 y ago modified 2026-06-17 4 mo ago also EUVD-2020-2647

cvss: 8.6; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 1.7%; EPSS 1.7% chance of exploitation in 30 days, percentile 77%
public exploits: 0; none known

The sync endpoint in YubiKey Validation Server before 2.40 allows remote attackers to replay an OTP. NOTE: this issue is potentially relevant to persons outside Yubico who operate a self-hosted OTP validation service with a non-default configuration such as an open sync pool; the issue does NOT affect YubiCloud.

Patch / fix

fixed in 1 links 1

yubico yubikey_one_time_password_validation_server 2.40

github.com/Yubico/yubikey-val/releases/tag/yubikey-val-2.40 release

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2020-10185 updated 2026-01-13 cvss 6.4

yubikey-val: allows remote attackers to replay an OTP

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.68% chance of exploitation in the next 30 days, higher than 77% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

yubico.com https://www.yubico.com/support/security-advisories/ysa-2020-01/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
NVD	3.1	8.6	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
NVD	2.0	6.8	AV:N/AC:M/Au:N/C:P/I:P/A:P

Classification

Weakness

CWE-294 Authentication Bypass by Capture-replay

References

yubico.com /support/security-advisories/ysa-2020-01/
exploit, vendor-advisory
github.com /Yubico/yubikey-val/releases/tag/yubikey-val-2.40
release-notes, third-party-advisory
lists.debian.org /debian-lts-announce/2020/03/msg00014.html
mailing-list

Sources

CVE List CVE-2020-10185
NVD CVE-2020-10185

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary