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.
CVE-2026-121506
HIGHPre-NVD 7.47.4
EchelonGraph scoreHIGH confidence
“—” beside the score: it is equal to the CVSS score beside it.
Score 7.4 from GitHub Security Advisory (severity: HIGH) published 2026-11-03. A secondary CVSS source baseline 7.4; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
Also known asEUVD-2026-115827 (ENISA EUVD) · GHSA-28fm-m2x6-h5pf (GitHub Security Advisories)Source: ENISA EUVD
7.4EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 7.4Exploit: None knownExposed services: Not assessed
A fix is available — apply it.
Fixed versions, as the CVE record's CNA (GitLab Inc.) states them: "Upgrade to version 1.2.5 or above."
- CVSS v3
- 7.4
- EG Score
- 7.4HIGHhigh confidence
- EG Risk
- 33EG Risk 33/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity74% × 45%Impact severity (EG Severity): CVSS 7.4 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation0.4% × 40%FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is available. Apply it within your standard update timelines. - EPSS PROB
- 0.4%
- EPSS %ILE
- 39th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.4): severity, escalated by confirmed exploitation. This CVE's 7.4 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.4 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.4% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-10). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
November 3, 2026
Last Modified
November 3, 2026
Advisory Details (2)
Auto-updated Nov 3, 2026Patch available.
Web page
Add length checks to fix fuzzer 393742176 (0a36941e) · Commits · NTPsec / ntpsec · GitLab
https://gitlab.com/NTPsec/ntpsec/-/commit/0a36941e499d533dfbc3fb6b1fcd8c367679d719Vendor Advisories for CVE-2026-121506(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Affected Packages
(3 across 3 ecosystems)
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| ntpsec | 1.2.2+dfsg1-1 ... 1.2.5+dfsg-1 (15 versions) |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| ntpsec | 1.2.3+dfsg1-8, 1.2.4+dfsg-1, 1.2.5+dfsg-1 |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| ntpsec | 1.2.3+dfsg1-8, 1.2.4+dfsg-1 |
| — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 8× in last 7d / 14× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed its CVE.org record (CNA or CISA ADP). An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). "EchelonGraph re-scored" is our own recompute of this CVE's score, not an update from a source, and is not counted in the refreshes above. Most recent first.
- 2026-11-13 16:50 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-12 16:33 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-11 16:38 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-11 05:06 UTCEchelonGraph re-scored
- 2026-11-11 05:06 UTCGHSA enrichmentGHSA-28fm-m2x6-h5pf · GitHub severity HIGH · GitHub CVSS 7.4
- 2026-11-10 16:42 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-09 16:34 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-08 16:38 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-07 16:38 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-06 16:36 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-05 16:36 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-04 16:34 UTCEPSS rescoreEPSS 0.4% · 39th percentile
- 2026-11-03 16:28 UTCEchelonGraph re-scored
- 2026-11-03 16:28 UTCGHSA enrichmentGHSA-28fm-m2x6-h5pf · GitHub severity HIGH · GitHub CVSS 7.4
- 2026-11-03 15:32 UTCEchelonGraph re-scored
- 2026-11-03 15:27 UTCEchelonGraph re-scored
- 2026-11-03 15:03 UTCENISA EUVD ID recordedEUVD-2026-115827 · Source: ENISA EUVD
- 2026-11-03 14:29 UTCEchelonGraph re-scoredFirst assessed: 7.4 HIGH
- 2026-11-03 14:26 UTCMITRE cvelistV5first tracked
Related CVEs(same product + same CWE)
Same product
10 shownDebian:12:ntpsec
Frequently asked(5)
What is CVE-2026-121506?
CVE-2026-121506 is a high-severity vulnerability; its CVE record was published on November 3, 2026. 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…
When was the CVE record for CVE-2026-121506 published?
The CVE record for CVE-2026-121506 was published on November 3, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of November 3, 2026; the record at its source may have been updated since.
Is CVE-2026-121506 actively exploited?
CVE-2026-121506 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (39th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-121506?
CVE-2026-121506 has a CVSS base score of 7.4 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-121506?
A fix for CVE-2026-121506 is available: update to the fixed version the vendor names in its advisory. Fixed versions, as the CVE record's CNA (GitLab Inc.) states them: "Upgrade to version 1.2.5 or above." The vendor advisories EchelonGraph has for CVE-2026-121506 are linked in the Vendor Advisories panel on this page.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-121506
Is Your Infrastructure Affected by CVE-2026-121506?
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