Evidence used
- No CISA KEV confirmation is currently recorded.
- EPSS is 0.87% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-40013High confidence
An attacker that has valid credentials can submit a Sieve script containing an extreme numeric literal, which causes an out-of-bounds write when the ManageSieve service compiles the script
Open-Xchange GmbH · OX Dovecot Pro
4.3MediumCVSS 3.1
Patch only the product branches with a verified fix
Fix availability varies by productMedium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 31 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityMedium→Operational priority:Medium, unchanged from published severity.unchanged
Compensating controls
- Apply the linked authoritative mitigation while planning the permanent fix.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs Open-Xchange GmbH OX Dovecot Pro and falls inside the recorded affected range.
- Recheck the vendor advisory before scheduling a change because no verified fixed version is currently retained.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Remediation availability differs by product scope
Verified remediation exists for at least one product or source, but 31 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
- Red Hat Product Security: 30 affected or under-investigation product states without a fixed product state in the same current advisory
- Debian Security Tracker: 1 affected package state with no published fix
Distribution package intelligence
5 package statesRelease-specific package status
Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
Package result overrides the generic status
BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 1 affected package state shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.
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 release | Source package | Vendor state | Fixed version | Evidence |
|---|---|---|---|---|
| Debian trixietrixie · source | dovecot | Vendor fix publishedDebian records a fixed source-package version for this release. | 1:2.4.1+dfsg1-6+deb13u7 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian bookwormbookworm · source | dovecot | Affected, no fix publishedDebian currently tracks this release as open. | Not published in this feed | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian forkyforky · source | dovecot | Vendor fix publishedDebian records a fixed source-package version for this release. | 1:2.4.5+dfsg1-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Debian sidsid · source | dovecot | Vendor fix publishedDebian records a fixed source-package version for this release. | 1:2.4.5+dfsg1-1 | Debian Security Tracker ↗Source updated 6 Oct 2026 |
| Ubuntu 24.04 LTSnoble · standard archive | dovecot | Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing. | Not published in this feed | Canonical Ubuntu Security ↗Source updated 6 Oct 2026 |
Direct vendor intelligence
1 currentAuthoritative 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.
CVE-2026-40013 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitydovecot: Dovecot: Denial of Service in ManageSieve service via crafted Sieve script
The vendor explicitly identifies these products as affected by this CVE.
- dovecot as a component of Red Hat Enterprise Linux 10
- dovecot-devel as a component of Red Hat Enterprise Linux 10
- dovecot-mysql as a component of Red Hat Enterprise Linux 10
- dovecot-pgsql as a component of Red Hat Enterprise Linux 10
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 10
- dovecot.src as a component of Red Hat Enterprise Linux 10
- dovecot as a component of Red Hat Enterprise Linux 6
- dovecot-devel as a component of Red Hat Enterprise Linux 6
- dovecot-mysql as a component of Red Hat Enterprise Linux 6
- dovecot-pgsql as a component of Red Hat Enterprise Linux 6
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 6
- dovecot.src as a component of Red Hat Enterprise Linux 6
- Summary
- A flaw was found in Dovecot. An authenticated attacker can submit a specially crafted Sieve script containing an extreme numeric literal to the ManageSieve service. This action triggers an out-of-bounds write during script compilation, leading to memory corruption and a crash of the ManageSieve process. This vulnerability results in a denial of service for script management and might also be leveraged for remote code execution.
- Remediation
- To mitigate this issue, disable the ManageSieve service if remote Sieve script management is not required. This can typically be achieved by removing `sieve` from the `protocols` setting in your Dovecot configuration (e.g., in `/etc/dovecot/dovecot.conf` or a file in `/etc/dovecot/conf.d/`). For example, change `protocols = imap pop3 lmtp sieve` to `protocols = imap pop3 lmtp`. After modifying the configuration, the Dovecot service must be restarted for the changes to take effect using `systemctl restart dovecot`. Disabling this service will prevent users from remotely managing their Sieve scripts.
Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority. Verified remediation exists for at least one product or source, but 31 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Fix availability varies by product01
What, why and how
An attacker that has valid credentials can submit a Sieve script containing an extreme numeric literal, which causes an out-of-bounds write when the ManageSieve service compiles the script. This causes memory corruption and an observed crash of the ManageSieve process, resulting in denial of service for script management. This might be able to be used for remote code execution. Disable the ManageSieve service if users do not need remote Sieve script management. Update to non-vulnerable version. No publicly available exploits are known.
What
An attacker that has valid credentials can submit a Sieve script containing an extreme numeric literal, which causes an out-of-bounds write when the ManageSieve service compiles the script. This causes memory corruption and an observed crash of the ManageSieve process, resulting in denial of service for script management. This might be able to be used for remote code execution. Disable the ManageSieve service if users do not need remote Sieve script management. Update to non-vulnerable version. No publicly available exploits are known.
Why
The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may execute code or commands in the affected security context.
What
An attacker that has valid credentials can submit a Sieve script containing an extreme numeric literal, which causes an out-of-bounds write when the ManageSieve service compiles the script. This causes memory corruption and an observed crash of the ManageSieve process, resulting in denial of service for script management. This might be able to be used for remote code execution. Disable the ManageSieve service if users do not need remote Sieve script management. Update to non-vulnerable version. No publicly available exploits are known.
Why
The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may execute code or commands in the affected security context.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.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 None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.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 → Buffer Underwrite ('Buffer Underflow') → execute code or commands in the affected security context
- Attack surface
- Network
- Privileges required
- Low: a basic authenticated account is required
- 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-124 ↗
CWE-124: Buffer Underwrite ('Buffer Underflow'). The product writes to a buffer using an index or pointer that references a memory location prior to the beginning of the buffer.
- 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:L/UI:N/S:U/C:N/I:N/A:LCommon 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.PRLowPrivileges required: The attacker needs basic user-level 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
- After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
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. - Fix availability varies by product
- Affected
- dovecot as a component of Red Hat Enterprise Linux 10
- dovecot-devel as a component of Red Hat Enterprise Linux 10
- dovecot-mysql as a component of Red Hat Enterprise Linux 10
- dovecot-pgsql as a component of Red Hat Enterprise Linux 10
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 10
- dovecot.src as a component of Red Hat Enterprise Linux 10
- dovecot as a component of Red Hat Enterprise Linux 6
- dovecot-devel as a component of Red Hat Enterprise Linux 6
- dovecot-mysql as a component of Red Hat Enterprise Linux 6
- dovecot-pgsql as a component of Red Hat Enterprise Linux 6
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 6
- dovecot.src as a component of Red Hat Enterprise Linux 6
- dovecot as a component of Red Hat Enterprise Linux 7
- dovecot-devel as a component of Red Hat Enterprise Linux 7
- dovecot-mysql as a component of Red Hat Enterprise Linux 7
- dovecot-pgsql as a component of Red Hat Enterprise Linux 7
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 7
- dovecot.src as a component of Red Hat Enterprise Linux 7
- dovecot as a component of Red Hat Enterprise Linux 8
- dovecot-devel as a component of Red Hat Enterprise Linux 8
- dovecot-mysql as a component of Red Hat Enterprise Linux 8
- dovecot-pgsql as a component of Red Hat Enterprise Linux 8
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 8
- dovecot.src as a component of Red Hat Enterprise Linux 8
- dovecot as a component of Red Hat Enterprise Linux 9
- dovecot-devel as a component of Red Hat Enterprise Linux 9
- dovecot-mysql as a component of Red Hat Enterprise Linux 9
- dovecot-pgsql as a component of Red Hat Enterprise Linux 9
- dovecot-pigeonhole as a component of Red Hat Enterprise Linux 9
- dovecot.src as a component of Red Hat Enterprise Linux 9
- Action
- Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
- Workaround
- To mitigate this issue, disable the ManageSieve service if remote Sieve script management is not required. This can typically be achieved by removing `sieve` from the `protocols` setting in your Dovecot configuration (e.g., in `/etc/dovecot/dovecot.conf` or a file in `/etc/dovecot/conf.d/`). For example, change `protocols = imap pop3 lmtp sieve` to `protocols = imap pop3 lmtp`. After modifying the configuration, the Dovecot service must be restarted for the changes to take effect using `systemctl restart dovecot`. Disabling this service will prevent users from remotely managing their Sieve scripts.
04
Evidence and provenance
Published 28 Aug 2026 · Last source change 28 Aug 2026, 15:54 UTC · CWE-124 · Buffer Underwrite ('Buffer Underflow')
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-29
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-67663
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD not scheduled
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- ENISA EUVD mappingEUVD-2026-67663 was added to the official ENISA EUVD mapping for this CVE.ENISA EUVD ↗
- Before
- not recorded
- After
- {"euvdId":"EUVD-2026-67663"}
- Catalogue recordCVE added to the BlackTree catalogue.CNA ↗
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.