Security readout for executives and security teams
Plain-English summary
An internet-reachable Xlight FTP Server running a version earlier than 3.9.5 could be compromised before login. A specially malformed SSH identification message can corrupt server memory, potentially allowing data theft, alteration, service disruption, or code execution. The supplied evidence does not establish active exploitation.
Executive priority
Prioritize immediate remediation of externally reachable systems, followed by internally exposed instances. The pre-authentication attack surface and potential confidentiality, integrity, and availability impact justify emergency handling. Avoid claiming a confirmed breach solely from this CVE; investigate suspicious crashes or connection patterns separately.
Technical view
A logic error in the SSH receive loop uses OR instead of AND in its termination condition. An unauthenticated remote client can send a malformed SSH identification string that writes beyond a heap buffer before authentication. CVE-2026-67191 is classified as CWE-122 with CVSS 3.1 score 9.8.
Likely exposure
Exposure is highest where Xlight FTP Server earlier than 3.9.5 accepts SSH or SFTP connections from untrusted networks. Authentication controls do not prevent exploitation because the vulnerable parsing occurs beforehand. The supplied sources do not provide deployment prevalence or observed target data.
Exploitation context
The vulnerability is remotely reachable, requires no privileges or user interaction, and has low stated attack complexity. However, it is not listed as KEV in the supplied bundle, and no cited evidence confirms exploitation in the wild. Treat exploitability as credible but active exploitation as unverified.
Researcher notes
The supplied record identifies a pre-authentication heap overwrite in SSH client-identification parsing and attributes it to an incorrect loop condition. It does not provide crash signatures, affected platform details, exploitation telemetry, or proof of reliable code execution. Validate exposure through version and service configuration without sending malformed traffic to production systems.
Mitigation direction
- Upgrade Xlight FTP Server to version 3.9.5 or later.
- Confirm the installed release and remediation guidance against the vendor changelog.
- Restrict SSH and SFTP access to trusted networks until upgrading.
- Disable SSH or SFTP service temporarily if operationally feasible and unnecessary.
- Monitor vendor and trusted vulnerability sources for updated guidance.
Validation and detection
- Inventory systems running Xlight FTP Server and record their exact versions.
- Identify whether SSH or SFTP is enabled and reachable from untrusted networks.
- Verify every affected installation reports version 3.9.5 or later after remediation.
- Review logs for unusual pre-authentication SSH connections, crashes, or service restarts.
- Confirm network restrictions prevent unauthorized access to remaining vulnerable instances.
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-122: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. 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 lookupCVE-2026-67191 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
- Critical
- CVSS
- 9.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
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.
SSVC decision data
CVSS vector scores
2 official scoresWe 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:U/C:H/I:H/A:H3.95.9VulnCheckCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N——VulnCheckVulnerability scoring details
Base CVSS 4.0 score
9.3CriticalVector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Base CVSS 3.1 score
9.8CriticalVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- ChangelogCVE reference, VulnCheck · release-notes
- https://www.vulncheck.com/advisories/xlight-ftp-server-pre-auth-heap-buffer-overflow-via-ssh-parserCVE reference, VulnCheck · third-party-advisory
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.
Heap-based Buffer Overflow
Heap-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.