CVE-2026-85185 Canonical · LXD

Path traversal in LXD btrfs storage driver allows arbitrary file deletion and write on host as root

Vulnerability at a glance

Severity, exploitation likelihood & attack requirements

CVSS v3.1 severity
9.6Critical
EPSS · exploitation likelihood
Not available No score available
EPSS trend
UnavailableNo comparable history
Known exploitation
Not in KEV CISA KEV catalog Absence does not establish safety
Attack vector
NetworkRemotely reachable
Attack complexity
LowFewer obstacles to exploitation
Privileges required
LowBasic privileges required
User interaction
NoneNo user action needed
Exploit availability & maturity
Not scored Availability not established No explicit exploit maturity assessment View exploit evidence
How to read the colors & trend
Higher exposureElevatedModerateLower exposureUnknown / unassessed

CVSS colors follow its reported severity. Attack-factor colors describe each requirement, not an overall risk rating. Gray also covers absence from KEV; absence does not establish safety.

EPSS display bands: below 1% blue, 1–10% amber, 10–50% orange, 50% and above red. These are presentation bands, not FIRST severity categories. The trend compares daily EPSS probabilities, not percentile ranks; “pp” means percentage points. The sparkline shows relative movement, with its vertical scale fitted to the observed scores.

Already protected by existing Atomicorp rules No new CVE-specific rule required.

Atomicorp ModSecurity protection

Protected by Atomicorp rules

Atomicorp ModSecurity rules block attacks exploiting this vulnerability when blocking is enabled. Keep your rules current.

By targeting underlying attack techniques and CWE weakness classes, existing rules can protect against newly disclosed vulnerabilities. Rule changes are regression-tested against attack and false-positive corpora.

2 rules identified Verified 2026-09-29 View rules & research details →

WAF protection applies to the tested attack paths; it does not change the CVSS or EPSS score. Keep your software patched and your Atomicorp rules current.

CISA SSVC assessment

CISA ADP · Assessed 2026-09-28 · SSVC 2.0.3

Exploitation
Proof-of-concept
Automatable
No
Technical Impact
Partial

Stakeholder-Specific Vulnerability Categorization records CISA’s assessment of exploitation, automation, and technical impact. “None reported” reflects the assessment date; it does not establish that no exploit exists. View SSVC source details.

On this page

CVE Details

  • Protection status: Protected by Atomicorp rules · About protection statuses
  • CVE: CVE-2026-85185
  • Name: Path traversal in LXD btrfs storage driver allows arbitrary file deletion and write on host as root
  • Severity: Critical
  • CVSS: 9.6 (v3.1) (Critical)
  • CVSS version: 3.1
  • CVSS source: canonical CNA
  • CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H
    • Attack vector: Network
    • Attack complexity: Low
    • Privileges required: Low
    • User interaction: None
    • Scope: Changed
    • Confidentiality impact: None
    • Integrity impact: High
    • Availability impact: High
  • CWE: CWE-22
  • Vendor: Canonical
  • Vulnerable product: LXD
  • CVE published: 2026-09-28
  • CVE last modified: 2026-09-28
  • Latest Update: 2026-09-29
  • Selected Rule IDs observed: 340006 , 390719
  • Matching rules: 2; rules with blocking actions: 2
  • Would-block Rule IDs: 340006 , 390719
  • Request surfaces inspected: Request filename, Request headers
Technical vulnerability details · CVSS assessments, exploit evidence & CPE data

CVSS assessments

CVSS v3.1 · security@ubuntu.com

  • Base score: 9.6
  • Base severity: CRITICAL
  • Exploitability subscore: 3.1
  • Impact subscore: 5.8
  • Assessment type: Secondary
  • Source identifier: security@ubuntu.com
  • Full vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H
    • Attack vector: Network
    • Attack complexity: Low
    • Privileges required: Low
    • User interaction: None
    • Scope: Changed
    • Confidentiality impact: None
    • Integrity impact: High
    • Availability impact: High
  • Exploit maturity: Not scored

Exploitability and impact subscores describe the vulnerability’s technical characteristics. Exploit maturity describes the reported state of exploitation; these are separate measures.

Assessment source: NVD record · CVE record

CISA SSVC assessments

These are CISA’s published decision points at the assessment time. They are not a complete organization-specific prioritization decision.

  • Provider: CISA ADP
  • Provider identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  • SSVC version: 2.0.3
  • Role: CISA Coordinator
  • Assessment timestamp: 2026-09-28T13:55:28.506443Z
  • Exploitation: poc
  • Automatable: no
  • Technical Impact: partial
  • Source: CISA ADP in the CVE record

Vulnerable CPE configurations

No vulnerable CPE configurations are supplied in the current NVD record. See the affected-product information and vendor guidance on this page.

Vulnerability Description

Path traversal in the btrfs storage driver in Canonical LXD versions 4.0.2 and later (fixed in 4.0.14, 5.0.10, 5.21.8 and 6.10) on Linux allows an authenticated client with permission to create instances in a project to delete arbitrary files on the host as root. On hosts whose root filesystem is btrfs, the client can also place attacker-controlled content at arbitrary host paths, leading to full host compromise. The client does this with a crafted subvolume path containing ../ sequences, sent in either of two ways: in the optimized_header.yaml of an optimized btrfs backup, or in the btrfs migration header sent by a malicious migration source.

  1. Maintain the observed Atomicorp protections. Keep your Atomicorp commercial rules current and confirm that the selected observed rules (340006 , 390719 ) have not been locally disabled. Atomicorp commercial rules are enabled by default. If you use Atomic WAF, review the applicable policy and rule settings.

  2. Apply the vendor’s remediation. WAF protection is defense in depth and does not replace upgrading or following the affected vendor’s guidance.

    • Affected versions: Canonical LXD versions earlier than 4.0.14.
    • Affected versions: Canonical LXD versions earlier than 5.0.10.
    • Affected versions: Canonical LXD versions earlier than 5.21.8.
    • Affected versions: Canonical LXD versions earlier than 6.10.
    • Recommended upgrade: Upgrade Canonical LXD to 4.0.14 or later.
    • Recommended upgrade: Upgrade Canonical LXD to 5.0.10 or later.
    • Recommended upgrade: Upgrade Canonical LXD to 5.21.8 or later.
    • Recommended upgrade: Upgrade Canonical LXD to 6.10 or later.
    • CNA guidance source: canonical
    • Vendor recommendation: Upgrade to LXD versions 4.0.14, 5.0.10, 5.21.8, 6.10 or later.

  3. Validate after changes. Confirm rule updates are current, review WAF events for the affected application, and test application behavior after vendor upgrades, mitigations, or local policy changes.

Research Notes

Atomicorp WAF protections are designed around attack techniques and exploit behaviors, allowing existing protections to apply across multiple vulnerabilities without requiring a unique rule for every CVE.

Public Vulnerability References

Test or Research Source

  • Source: Atomicorp AI Research Framework
  • Tags: cve, derived, traversal, waf-probe

Research Note Context

This research note documents exploit-technique analysis associated with this vulnerability and references Atomicorp WAF protections observed during engineering review, testing, or validation activities.

Atomicorp security controls are generally designed to identify and mitigate attack techniques and exploit behaviors rather than individual CVE identifiers. As a result, protections developed for one vulnerability may also apply to related attack variants and future vulnerabilities using similar techniques.

Learn More

Atomicorp develops commercially supported security technologies for web applications, servers, endpoints, workloads, and legacy enterprise platforms.

Organizations interested in protecting systems against exploit techniques associated with vulnerabilities such as this one can learn more about:

  • Atomic ModSecurity Rules: commercially maintained WAF rules for ModSecurity deployments, including protections for web attacks, bots, scanners, malware, exploitation attempts, and emerging vulnerability classes.
  • Atomic WAF: an enterprise web application firewall with Atomicorp rules, centralized management, reporting, authentication controls, and operational tooling.
  • Atomic ModSecurity Integrator: a special licensing option for MSPs, MSSPs, OEMs, VARs, reverse proxy providers, and other integrators who want to incorporate Atomicorp ModSecurity rule technology into their own products or services.
  • Atomic OSSEC: an enterprise OSSEC-based intrusion detection, compliance, and security monitoring platform.
  • Atomic Protector: workload protection for Linux, web, cloud, data center, and hybrid environments.

For additional information, product evaluations, or technical discussions, visit https://www.atomicorp.com/ or https://modsecurity.io/ .