cbcvebase.
CVE-2026-42010
published 2026-05-07

CVE-2026-42010: A flaw was found in gnutls. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) wrongfully matched usernames containing a NUL character…

PriorityP272critical9.8CVSS 3.1
AVNACLPRNUINSUCHIHAH
EPSS
1.05%
64.0th percentile
A flaw was found in gnutls. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) wrongfully matched usernames containing a NUL character with truncated usernames. A remote attacker could exploit this by sending a specially crafted username, leading to an authentication bypass. This vulnerability allows an attacker to gain unauthorized access by circumventing the authentication process.

Affected

8 ranges
VendorProductVersion rangeFixed in
gnugnutls——
redhatenterprise_linux——
redhatenterprise_linux——
redhatenterprise_linux——
redhatenterprise_linux——
redhatenterprise_linux——
redhatopenshift_container_platform——
ubuntugnutls28——

Detection & IOCsextracted from sources · hover to see the quote

  • →Target servers using RSA-PSK (RSA Pre-Shared Key) TLS cipher suites in GnuTLS — these are the only configurations vulnerable to this authentication bypass. ↗
  • →Detect authentication attempts where the supplied PSK username contains an embedded NUL (0x00) byte — this is the crafted payload pattern used to trigger the bypass. ↗
  • ·Only GnuTLS servers explicitly configured to use RSA-PSK cipher suites are vulnerable. Servers not using RSA-PSK are not affected by this bypass. ↗
  • ·The root cause is a string comparison that stops at the first NUL byte rather than comparing the full username length. The fix requires updating GnuTLS to a version that performs comparison up to the full username length. ↗

CVSS provenance

nvdv3.19.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
vendor_ubuntu9.1CRITICAL
vendor_redhat7.1HIGH
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