CVE-2026-107566

MEDIUMPre-NVD 6.56.5
EchelonGraph scoreHIGH confidence

“—” beside the score: it is equal to the CVSS score beside it.

Score 6.5 from GitHub Security Advisory published 2026-10-19. A secondary CVSS source baseline 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
Trending — 3 sources updated this week

Also known asEUVD-2026-104408 (ENISA EUVD) · GHSA-87p7-4v38-33c9 (GitHub Security Advisories)Source: ENISA EUVD

6.5EG
EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 6.5Exploit: None knownExposed services: Not assessed

Upgrade to hMailServer 6.3.7, which refuses a Sieve script that adds or deletes From, Sender, Resent-From, Resent-Sender or DKIM-Signature when the script is stored, and does not make such an edit at delivery for a scri… (from the CVE record's solution, GitLab Inc.) — apply it.

Missing authorization in the Sieve editheader action (6.2.22 through 6.3.6) and in the mail-rule Set header value action (6.0.0 through 6.3.6) of Progressive Robot hMailServer allows an authenticated user to make the server send mail as any address, DKIM-signed where the address is at a domain the server signs for. A Sieve script's editheader (addheader/deleteheader) could add or delete any header field except Received and Return-Path, and the server applies a script's header edits before it queues a redirect, so the redirected copy is sent as the script left it. The server signs a message's first delivery pass as the domain named in its From header wherever it signs DKIM for that domain and the message carries no signature of it. A script could therefore delete and re-add From - another account's address, or anyone's at a hosted domain - and redirect, so the server sent the message in that name and, for a hosted domain, signed it with that domain's DKIM key, a forgery aligned to pass the domain's DMARC; or, where another sender's domain is one the server signs for, delete the DKIM-Signature that sender's message arrived with, alter a field, and redirect, so the server re-signed the altered message as that sender's domain. editheader placed no restriction on From, Sender, Resent-From, Resent-Sender or DKIM-Signature. The editheader action was introduced in 6.2.22. In the mail-rule engine, a domain's or an account's rule's Set header value action could likewise set From, Sender, Resent-From, Resent-Sender or DKIM-Signature ahead of a forward or a copy, whoever the rule belonged to, so that an account acting on its own rules over COM, a domain administrator, or an API key confined to a domain (over the REST API from 6.3.4) could have the server forward or copy a message in the name of any address, signed, where that address is at a domain the server hosts with DKIM signing enabled, with that domain's key.

CVSS v3
6.5
EG Score
6.5MEDIUMhigh confidence
EG Risk
29
EG Risk 29/100

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)
Severity65% × 45%
Impact severity (EG Severity): CVSS 6.5 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.2% × 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: Upgrade to hMailServer 6.3.7, which refuses a Sieve script that adds or deletes From, Sender, Resent-From, Resent-Sender or DKIM-Signature when the script is stored, and does not make such an edit at delivery for a scri… (from the CVE record's solution, GitLab Inc.). Apply it within your standard update timelines.
EPSS PROB
0.2%
EPSS %ILE
7th
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 (6.5): severity, escalated by confirmed exploitation. This CVE's 6.5 is its impact severity (EG Severity), not escalated.

EG Severity
6.5 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-24). 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: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

Upgrade to hMailServer 6.3.7, which refuses a Sieve script that adds or deletes From, Sender, Resent-From, Resent-Sender or DKIM-Signature when the script is stored, and does not make such an edit at delivery for a scri… (from the CVE record's solution, GitLab Inc.). 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.

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 19, 2026

Last Modified

October 20, 2026

Advisory Details (2)

Auto-updated Oct 19, 2026
Fix named in the CVE record's solution (GitLab Inc.).
Web page

Sieve editheader and mail-rule Set header value: a script, or a domain's or an account's rule, could rewrite From, Sender and DKIM-Signature and then redirect or forward, so the server sent and DKIM-signed a message as any address (6.0.0-6.3.6) (#83) · Issues · hmailserver / hMailServer · GitLab

https://gitlab.com/hmailserver/hmailserver/-/work_items/83
Web page

hMailServer 6.3.7 · hmailserver / hMailServer · GitLab

https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.7

Vendor Advisories for CVE-2026-107566(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 9× in last 7d / 22× 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.

  1. 2026-10-30 16:33 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  2. 2026-10-29 16:32 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  3. 2026-10-28 17:55 UTCOSV refresh
  4. 2026-10-28 16:31 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  5. 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  6. 2026-10-26 16:30 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  7. 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  8. 2026-10-25 14:54 UTCEG score recompute
  9. 2026-10-24 16:32 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  10. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  11. 2026-10-22 16:33 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  12. 2026-10-21 16:32 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  13. 2026-10-20 20:26 UTCEG score recompute
  14. 2026-10-20 20:26 UTCGHSA enrichmentGHSA-87p7-4v38-33c9 · GitHub CVSS 6.5
  15. 2026-10-20 19:28 UTCEG score recompute
  16. 2026-10-20 19:28 UTCGHSA enrichmentGHSA-87p7-4v38-33c9 · GitHub CVSS 6.5
  17. 2026-10-20 16:32 UTCEPSS rescoreEPSS 0.2% · 7th percentile
  18. 2026-10-19 21:50 UTCEG score recompute
  19. 2026-10-19 21:50 UTCGHSA enrichmentGHSA-87p7-4v38-33c9 · GitHub CVSS 6.5
  20. 2026-10-19 16:37 UTCEG score recompute
  21. 2026-10-19 15:49 UTCEG score recomputeFirst assessed: 6.5 MEDIUM
  22. 2026-10-19 15:47 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-107566?
CVE-2026-107566 is a medium-severity vulnerability; its CVE record was published on October 19, 2026. Missing authorization in the Sieve editheader action (6.2.22 through 6.3.6) and in the mail-rule Set header value action (6.0.0 through 6.3.6) of Progressive Robot hMailServer allows an authenticated user to make the server send mail as any address, DKIM-signed where the address is at a domain the…
When was the CVE record for CVE-2026-107566 published?
The CVE record for CVE-2026-107566 was published on October 19, 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 20, 2026; the record at its source may have been updated since.
Is CVE-2026-107566 actively exploited?
CVE-2026-107566 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (7th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-107566?
CVE-2026-107566 has a CVSS base score of 6.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-107566?
The CVE record's solution for CVE-2026-107566, written by its CNA GitLab Inc., names the fix: "Upgrade to hMailServer 6.3.7, which refuses a Sieve script that adds or deletes From, Sender, Resent-From, Resent-Sender or DKIM-Signature when the script is stored, and does not make such an edit at delivery for a scri…" The vendor advisories EchelonGraph has for CVE-2026-107566 are linked in the Vendor Advisories panel on this page.

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