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    CVE-2026-121506

    An out-of-bounds read and write in NTS client extension field parsing (extens_client_recv) in NTPsec before 1.2.5 allows a remote attacker who can send NTP server-mode replies to an NTS client to corrupt heap memory and crash ntpd, and, combined with the NTS-KE client out-of-bounds read fixed in 1.2.4, to bypass NTS authentication and set the client's time, via an NTS Authenticator and Encrypted Extension Fields field whose nonce length exceeds the field.

    Published:Nov 3, 2026
    Last Modified:Nov 3, 2026
    EPS:Nov 3, 2026
    EPSS Score:
    CVSS Score:7.4

    Affected Products

    Vendor
    Ntpsec
    Product
    Ntpsec

    Exploits

    No exploit reference

    Common Weakness Enumeration

    CWE-787 Out-of-bounds Write

    Common Attack Pattern Enumeration and Classification (CAPEC)

    No CAPEC recorded yet

    Related CVEs

    CVE-2026-121505 (CVSS 3.7) — An out-of-bounds read in the NTS-KE client response parser (nts_client_process_response_core) in NTPsec before…
    CVE-2026-102486 (CVSS 7.5) — Out-of-bounds read in NTS extension field parsing in NTPsec ntpd 1.1.4 through 1.2.5 allows a remote attacker …
    CVE-2026-102485 (CVSS 5.2) — Out-of-bounds read in the Motorola Oncore refclock driver in NTPsec ntpd before 1.2.6 allows an attacker who c…
    CVE-2026-102484 (CVSS 6.4) — Heap-based buffer overflow in the JJY refclock driver in NTPsec ntpd before 1.2.6 allows an attacker who contr…
    CVE-2026-102483 (CVSS 7.5) — Reachable exit in NTPsec ntpd 1.1.4 through 1.2.5 allows a remote attacker to terminate the daemon via an NTS …
    CVE-2026-18321 (CVSS 4.7) — Buffer overflow in NTPsec's Zyfer refclock allows local attacker to crash ntpd…
    CVE-2023-4012 (CVSS 7.5) — ntpd will crash if the server is not NTS-enabled (no certificate) and it receives an NTS-enabled client reques…
    CVE-2021-22212 (CVSS 4) — ntpkeygen can generate keys that ntpd fails to parse. NTPsec 1.2.0 allows ntpkeygen to generate keys with '#' …
    CVE-2019-6442 (CVSS 6.5) — An issue was discovered in NTPsec before 1.1.3. An authenticated attacker can write one byte out of bounds in …
    CVE-2019-6443 (CVSS 9.1) — An issue was discovered in NTPsec before 1.1.3. Because of a bug in ctl_getitem, there is a stack-based buffer…

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High