Mailu is a mail server distributed as a set of Docker images. Prior to f05aeb8322e2f61096af6b089d61ba6f40587d96, domain managers can enable spoofing for hosted domains they do not control. A potentially malicious domain administrator enables spoofing for another hosted domain and can send emails that are authenticated with DKIM/SPF for domains they should not be able to. This vulnerability is addressed by f05aeb8322e2f61096af6b089d61ba6f40587d96.
CVE-2026-86009
HIGHPre-NVD 8.28.2Trending — 3 sources updated this weekElevatedEG-KEV Tier 3: ElevatedEG-KEV is EchelonGraph's own tiering of exploitation signals from CISA KEV, CISA's SSVC data (Vulnrichment), ransomware data, public exploit-code references and EPSS.Tier 3 is not evidence of exploitation. It means public exploit code is referenced, or CISA's SSVC data says "public PoC", or EPSS ranks the CVE in the top 5%.Signals for this CVE: CISA's SSVC exploitation value: public PoC.EchelonGraph confidence 38%: a heuristic from the tier and the number of signals, not a measured probability.
EchelonGraph scoreMEDIUM confidence
“—” beside the score: it is equal to the CVSS score beside it.
This high-severity CVE scores 8.2 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3% (21st percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.
Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
8.2EG
EchelonGraph verdictPlan mitigationRemediate within your standard update timelines (the SSVC decision on this page).
- CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 8.2Exploit: No code on recordExposed services: Not assessed
No fix is confirmed yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for the fix.
- CVSS v3
- 8.2
- EG Score
- 8.2HIGHmedium confidence
- EG Risk
- 53EG Risk 53/100
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)Severity82% × 45%Impact severity (EG Severity): CVSS 8.2 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation40% × 40%EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.Automatability0% × 15%CISA's SSVC Automatable value: no (Vulnrichment).SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).Exploitation public PoC (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: No fix is confirmed yet. Restrict network exposure of the affected system within your standard update timelines, and watch for a fix. - EPSS PROB
- 0.3%
- EPSS %ILE
- 21st
- 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 (8.2): severity, escalated by confirmed exploitation. This CVE's 8.2 is its impact severity (EG Severity), not escalated.
- EG Severity
- 8.2 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.a secondary CVSS source · CVSS v3.0 or v3.1
- EG Likelihood
- 0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-20). 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 low or medium mission impact; Track* at high (mission-essential systems).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: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
No fix is confirmed yet. Restrict network exposure of the affected system within your standard update timelines, and watch for a fix.
Exploitation public PoC (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.
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
October 16, 2026
Last Modified
October 21, 2026
Advisory Details (4)
Auto-updated Oct 16, 2026No fix on record yet. Sources: github, github_pr, github_commit.
GitHub commit
commit f05aeb8322e2 (Mailu/Mailu)
Fix landed in Mailu/Mailu commit f05aeb8322e2 — awaiting tagged release
https://github.com/Mailu/Mailu/commit/f05aeb8322e2f61096af6b089d61ba6f40587d96GitHub pull request
internal: scope allow_spoofing to the sender's own domain (#2686)
Fix merged in Mailu/Mailu PR #4072 on 2026-07-20 — awaiting tagged release
https://github.com/Mailu/Mailu/pull/4072Web page
Domain managers can allow themself and other users to spoof on other domains · Issue #2686 · Mailu/Mailu · GitHub
https://github.com/Mailu/Mailu/issues/2686GitHub advisoryMentions a patch (unverified)
Domain managers can allow themselves to spoof hosted domains they do not control · Advisory · Mailu/Mailu · GitHub
https://github.com/Mailu/Mailu/security/advisories/GHSA-crww-m82r-2wfmWeakness Classification(2)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 12× in last 7d / 12× 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 it from the CNA feed. 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). Most recent first.
- 2026-10-21 16:34 UTCEPSS rescoreEPSS 0.3% · 21st percentile
- 2026-10-21 03:27 UTCEG score recompute
- 2026-10-21 02:33 UTCEG score recompute
- 2026-10-20 17:57 UTCEG score recompute
- 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.3% · 21st percentile
- 2026-10-19 16:33 UTCEPSS rescoreEPSS 0.3% · 21st percentile
- 2026-10-18 16:33 UTCEPSS rescoreEPSS 0.3% · 20th percentile
- 2026-10-18 03:05 UTCEG score recompute
- 2026-10-17 16:35 UTCEPSS rescoreEPSS 0.3% · 20th percentile
- 2026-10-16 17:54 UTCEG score recompute
- 2026-10-16 16:35 UTCEG score recomputeFirst assessed: 8.2 HIGH
- 2026-10-16 16:28 UTCMITRE cvelistV5first tracked
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Frequently asked(5)
What is CVE-2026-86009?
CVE-2026-86009 is a high-severity vulnerability; its CVE record was published on October 16, 2026. Mailu is a mail server distributed as a set of Docker images. Prior to f05aeb8322e2f61096af6b089d61ba6f40587d96, domain managers can enable spoofing for hosted domains they do not control. A potentially malicious domain administrator enables spoofing for another hosted domain and can send emails…
When was the CVE record for CVE-2026-86009 published?
The CVE record for CVE-2026-86009 was published on October 16, 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 October 21, 2026; the record at its source may have been updated since.
Is CVE-2026-86009 actively exploited?
CVE-2026-86009 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (21st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-86009?
CVE-2026-86009 has a CVSS base score of 8.2 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-86009?
No fix for CVE-2026-86009 is confirmed yet. Until one is published, restrict network exposure of the affected system — for example, keep it off the internet or limit it to trusted networks — and watch for a fix.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-86009
Is Your Infrastructure Affected by CVE-2026-86009?
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