Security readout for executives and security teams
Plain-English summary
Mailpit versions before 1.28.3 can be tricked into making unintended server-side web requests while checking HTML email content. This matters because Mailpit may be able to reach internal services that a remote user cannot. The reported impact is limited information exposure, with medium CVSS severity.
Executive priority
Treat as a timely developer-tool update, not an emergency. Prioritize internet-facing or shared Mailpit deployments first, especially where the host has access to sensitive internal systems. Upgrade to 1.28.3 or later during the next security maintenance window.
Technical view
CVE-2026-23845 is a CWE-918 SSRF in Mailpit’s HTML Check API, specifically CSS downloading during HTML compatibility analysis. The inlineRemoteCSS() behavior downloads external CSS referenced by HTML email stylesheet links. Affected versions are axllent Mailpit before 1.28.3. CVSS v3.1 is 5.8: network exploitable, low complexity, no privileges or user interaction, changed scope, low confidentiality impact.
Likely exposure
Exposure is most relevant where Mailpit is reachable by untrusted users or automated systems that can submit or trigger HTML email analysis. Risk increases if the Mailpit host can access internal metadata services, admin panels, or other private network resources.
Exploitation context
The source bundle does not report active exploitation, and this CVE is not marked in KEV. Exploitation depends on the attacker being able to cause Mailpit’s HTML Check API to process crafted HTML that references remote CSS resources.
Researcher notes
Evidence is limited to the CVE record, GitHub advisory, fixing commit, and 1.28.3 release. No public exploitation evidence is provided in the supplied sources. Avoid assuming impact beyond SSRF-driven low confidentiality exposure unless local network reachability creates higher business risk.
Mitigation direction
- Upgrade Mailpit to version 1.28.3 or later.
- If upgrade is delayed, check the vendor advisory for supported guidance.
- Restrict access to Mailpit and its API to trusted users and networks.
- Review outbound network access from Mailpit to sensitive internal services.
Validation and detection
- Inventory all Mailpit deployments and confirm installed versions.
- Identify any Mailpit instance below version 1.28.3.
- Confirm whether HTML Check API is reachable by untrusted users or automation.
- Review network paths from Mailpit hosts to internal-only services.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-918: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCloud metadata behavior lookup
The CVE wording references SSRF or metadata access, so cloud discovery and credential material review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-23845 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 5.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N3.91.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.8MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/axllent/mailpit/security/advisories/GHSA-6jxm-fv7w-rw5jCVE reference · x_refsource_CONFIRM
- https://github.com/axllent/mailpit/commit/1679a0aba592ebc8487a996d37fea8318c984dfeCVE reference · x_refsource_MISC
- https://github.com/axllent/mailpit/releases/tag/v1.28.3CVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Server-Side Request Forgery (SSRF)
Server-Side Request Forgery (SSRF) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.