CVE-2026-34179: LXD: Update of type field in restricted TLS certificate allows privilege escalation to cluster admin

Should you act?

Critical, preconditions apply

Severe if exploited, but exploitation needs conditions that may not apply to you. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 35: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 35% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Needs an account (high (admin)). Exposure depends on who can log in.
• Only applies if your dependency tree includes github.com/canonical/lxd (Go) >= 0.0.0-20210305023314-538ac3df036e, <= 0.0.0-20260226085519-736f34afb267, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

In Canonical LXD versions 4.12 through 6.7, the doCertificateUpdate function in lxd/certificates.go does not validate the Type field when handling PUT/PATCH requests to /1.0/certificates/{fingerprint} for restricted TLS certificate users, allowing a remote authenticated attacker to escalate privileges to cluster admin.

From the GitHub advisory

Summary

A restricted TLS certificate user can escalate to cluster admin by changing their certificate type from client to server via PUT/PATCH to /1.0/certificates/{fingerprint}. The non-admin guard and reset block in doCertificateUpdate fail to validate or reset the Type field, allowing a caller-supplied value to persist to the database. The modified certificate is matched as a server certificate during TLS authentication, granting ProtocolCluster with full admin privileges.

Details

doCertificateUpdate in lxd/certificates.go handles PUT/PATCH requests to /1.0/certificates/{fingerprint} for both privileged and unprivileged callers. The access handler is allowAuthenticated, so any trusted TLS user (including restricted) can reach this code.

For unprivileged callers (restricted users who fail the EntitlementCanEdit check at line 975), two defenses are intended to prevent field tampering:

Weakness type: CWE-915.

Product: github.com/canonical/lxd (Go) · Assigned by: canonical · Published: 2026-04-09

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: high (admin)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.42% probability of exploitation activity in the next 30 days; percentile 35.

Timeline

• 2026-04-09 — CVE record last updated
• 2026-04-09 — CVE record published by canonical
• 2026-04-10 — GitHub-reviewed advisory GHSA-c3h3-89qf-jqm5 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Update of type field in restricted TLS certificate allows privilege escalation to cluster admin github.com
2. Improve validation on certificate edit github.com

Vulnerability records

1. GitHub Advisory GHSA-c3h3-89qf-jqm5 github.com
2. CVE.org record CVE-2026-34179 cve.org
3. NVD entry CVE-2026-34179 nvd.nist.gov

Critical Go advisories · Today’s Security Digest