Out-of-bounds Write in NTPsec
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 1.2.5
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 1.2.5.
- Exploitation0/40No signal
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Data gap: No advisory context yet
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity7.4/10CVSS 7.4
- No patch0/5No signal
What would change the score
- Would score about 69 if added to CISA KEV
- Would score about 64 if CISA's SSVC rates exploitation active
- Would score about 29 if advisories confirm default setups are exposed
CVE-2026-121506 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.4 (high) and affects NTPsec; fixed in 1.2.5.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 24/100 · provisional
- Fix
- Fixed in 1.2.5
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: no
- Technical impact: partial
Summary
NTPsec, an open-source implementation of the Network Time Protocol used to keep computer clocks synchronized, is affected when it runs as an NTS client. A remote attacker who can send crafted server replies can corrupt memory and crash the time daemon, and in combination with a related flaw, can bypass NTS authentication and set the client's clock to a false time.
Read the original description
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.
What to do
Upgrade to a fixed version: 1.2.5.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: no · Technical impact: partial
- Record last updated
Affected versions
- NTPsec NTPsec
From 1.1.4 · fixed in 1.2.5
Evidence 2
- Link
- Link
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-121506
Is CVE-2026-121506 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-121506?
NTPsec: from 1.1.4 before 1.2.5.Source: cve.now feed data
How do I fix CVE-2026-121506?
Upgrade to a fixed version: 1.2.5.Source: cve.now feed data