BlackTreeCVE Intelligence
← Back to the CVE catalogue
Full vulnerability report · 2026
CVE-2025-59028High confidence

Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins

Open-Xchange GmbH · OX Dovecot Pro

5.3MediumCVSS 3.1
Recommended action
Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
R
Operational reassessment

Published severity in operational context

Open reassessment dashboard →
Published severityMediumOperational priority:Medium, unchanged from published severity.unchanged

Evidence used

  • No CISA KEV confirmation is currently recorded.
  • The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
  • EPSS is 0.45% for the current model date.

Compensating controls

  • Validate the affected product branch and deploy the verified fixed release.
  • Restrict the affected network interface to trusted sources where business-safe.
  • Monitor vendor guidance and exploitation sources for a material change.

Verification

  1. Confirm that the asset runs Open-Xchange GmbH OX Dovecot Pro and falls inside the recorded affected range.
  2. Verify the installed build against the product-specific fixed version after deployment.
  3. Validate exposure, authentication requirements and compensating controls in the actual environment.
  4. Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Mitigation target: As exposure requiresRemediation target: Within 365 days

This automated reassessment organises public evidence. It does not know asset exposure, business impact or control effectiveness and does not replace CVSS or a human risk decision.

Distribution package intelligence

Release-specific package status

Alpine, Debian findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.

5 package states
Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Distribution releaseSource packageVendor stateFixed versionEvidence
Alpine v3.23v3.23 · maindovecotVendor fix publishedAlpine records a security fix at this version. An absent entry does not mean the package is unaffected.2.4.3-r0Alpine Security Database ↗Source updated 3 Oct 2026
Debian trixietrixie · sourcedovecotVendor fix publishedDebian records a fixed source-package version for this release.1:2.4.1+dfsg1-6+deb13u4Debian Security Tracker ↗Source updated 6 Oct 2026
Debian bookwormbookworm · sourcedovecotNot affectedDebian marks this release not affected (fixed-version marker 0).Not published in this feedDebian Security Tracker ↗Source updated 6 Oct 2026
Debian forkyforky · sourcedovecotVendor fix publishedDebian records a fixed source-package version for this release.1:2.4.3+dfsg1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Debian sidsid · sourcedovecotVendor fix publishedDebian records a fixed source-package version for this release.1:2.4.3+dfsg1-1Debian Security Tracker ↗Source updated 6 Oct 2026
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
OXDC-ADV-2026-0001 · CSAF 2.0 · revision 2 · finalOpen-Xchange GmbHInvalid base64 authentication can cause DoS for other logins
2 last affected

The vendor identifies these as the last affected versions before a fixed or unaffected line.

  • OX Dovecot Pro 3.1.0
  • OX Dovecot CE 2.4.0
Summary
When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail.
Remediation
Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments).
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2025-209088

No EUVD known-exploited evidence

ENISA has published the identifier mapping but no EUVD description has been stored yet.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
Not supplied in the stored EUVD record
Advisory evidence
No linked advisory details stored yet
Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Patch available
01

What, why and how

When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail. Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins. Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments). No publicly available exploits are known.

What

When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail. Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins. Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments). No publicly available exploits are known.

Why

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

What

When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all active authentication sessions to fail. Invalid BASE64 data can be used to DoS a vulnerable server to break concurrent logins. Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments). No publicly available exploits are known.

Why

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may cause the confidentiality, integrity or availability impact described by the vendor.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Improper Input Validation → cause the confidentiality, integrity or availability impact described by the vendor
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-20 ↗

CWE-20: Improper Input Validation. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.ALowAvailability impact: A successful attack can cause a limited loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedCWE-20
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

BSI · German · WID-SEC-2026-0891Dovecot: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Dovecot ausnutzen, um SQL-Injection-Angriffe durchzuführen, die Authentifizierung zu umgehen, vertrauliche Informationen offenzulegen oder einen Denial-of-Service-Zustand herbeizuführen.

Official advisory ↗
Cyber Security Agency of Singapore · English · CSA-SB-20260401Security Bulletin 01 Apr 2026

The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 01 Apr 2026, published on 1 April 2026. Open the linked bulletin for the product, severity and reference information published in that issue.

Official advisory ↗
JVN iPedia · Japanese · JVNDB-2026-014348Timo Sirainen等の複数ベンダの製品における入力確認に関する脆弱性

無効なbase64 SASLデータを送信すると、認証サーバーがログインプロセスを切断し、すべてのアクティブな認証セッションが失敗します。無効なBASE64データは、脆弱なサーバーに対してDoS攻撃を行い、同時ログインを妨害するために使用できます。修正バージョンをインストールするか、ログインプロセスの同時実行を無効にしてください（大規模な展開では大きなパフォーマンスペナルティが生じます）。公開されているエクスプロイトは知られていません。

Official advisory ↗
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
Fixed
Action
Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments).
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 27 Mar 2026 · Last source change 27 Mar 2026, 19:43 UTC · CWE-20 · Improper Input Validation

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2025-209088
Product sourceVendor CSAF · Open-Xchange GmbH
Remediation sourceVendor CSAF · Open-Xchange GmbH
CWE sourceCNA
NVD statusNVD enriched

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates ↗
  1. Affected versionsThe structured affected or fixed version information changed.
    Before
    OX Dovecot Pro: ≤ 3.1.0, ≤ 2.4.0 · Fixed: Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments).
    After
    OX Dovecot Pro: ≤ 3.1.0, ≤ 2.4.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CNA ↗
  2. Vendor guidanceAuthoritative vendor guidance changed: removed remediation: documentation.open-xchange.com/oxdc-adv-2026-0001.md.
    Before
    remediation: documentation.open-xchange.com/oxdc-adv-2026-0001.md · vendor advisory: documentation.open-xchange.com/oxdc-adv-2026-0001.json
    After
    vendor advisory: documentation.open-xchange.com/oxdc-adv-2026-0001.json
    security@open-xchange.com ↗
  3. Affected versionsThe structured affected or fixed version information changed.
    Before
    ≤ 3.1.0; ≤ 2.4.0 · Fixed: Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments).
    After
    OX Dovecot Pro: ≤ 3.1.0, ≤ 2.4.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    CNA ↗
  4. Remediation statusRemediation status changed from Patch available to Awaiting fix.
    Before
    Patch available
    After
    Awaiting fix
    security@open-xchange.com ↗
  5. Affected versionsThe structured affected or fixed version information changed.
    Before
    OX Dovecot Pro: ≤ 3.1.0, ≤ 2.4.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    OX Dovecot Pro: ≤ 3.1.0, ≤ 2.4.0 · Fixed: Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments).
    Open-Xchange GmbH ↗
  6. Affected versionsThe structured affected or fixed version information changed.
    Before
    ≤ 3.1.0; ≤ 2.4.0 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
    After
    ≤ 3.1.0; ≤ 2.4.0 · Fixed: Install fixed version or disable concurrency in login processes (heavy perfomance penalty on large deployments).
    Open-Xchange GmbH ↗
  7. Remediation statusRemediation status changed from Awaiting fix to Patch available.
    Before
    Awaiting fix
    After
    Patch available
    Open-Xchange GmbH ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
Fixed release recorded from official guidance
ENISA EUVD · EUVD-2025-209088↗Open-Xchange GmbH security advisory↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2025-59028 · cve.blacktree.nl