How severe is CVE-2026-55866?

CVE-2026-55866 has a CVSS score of 3.7/10, rated LOW. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-55866?

CVE-2026-55866 affects the following packages: github.com/authzed/spicedb (Go). Ecosystems affected: Go.

How do I fix CVE-2026-55866?

Update github.com/authzed/spicedb to 1.54.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55866 is resolved across your whole dependency graph.

How do I detect CVE-2026-55866 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/authzed/spicedb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-55866 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2026-55866 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-55866 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-55866?

CVE-2026-55866 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 28th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-55866?

CVE-2026-55866 is classified as CWE-863 (CWE-863). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-55866 published, and has it been updated?

CVE-2026-55866 was published on September 14, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

LOW severity

CVE-2026-55866 — spicedb

LOWFix: authzed/spicedb@44a1c9f

CVE-2026-55866 is a low-severity (CVSS 3.7) CWE-863 vulnerability in github.com/authzed/spicedb. A fix is available for github.com/authzed/spicedb — see the affected versions and patch details below.

SpiceDBChecks involving relations with caveats can result in unconditional permission when conditional permission is expected

Also known asGHSA-4vrg-r928-h5vvGO-2026-5133

Published

Sep 14, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 31, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-55866.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs28th percentile — riskier than 28% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/authzed/spicedb

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Under concurrency, CheckPermission and CheckBulkPermissions can return PERMISSIONSHIP_HAS_PERMISSION for a (resource, permission, subject) whose correct answer is PERMISSIONSHIP_CONDITIONAL_PERMISSION.

You are impacted if all of the following hold:

Your schema has a permission combining relations with an intersection or exclusion, where a subject reaches it through a caveated branch and a non-caveated branch. For example:

  definition user {}

  caveat some_caveat(somecondition int) { somecondition == 42 }

  definition document {
    relation reader: user | user with some_caveat
    relation writer: user
    relation banned: user
    permission has_permission = (reader & writer) - banned
  }

A subject reaches the permission via the caveated edge:

  document:firstdoc#reader@user:caveatedreader[some_caveat]
  document:firstdoc#writer@user:caveatedreader

Your workload issues LookupResources with a context request parameter, concurrently with CheckPermission/CheckBulkPermissions for the same subject/resource, and
The dispatch result cache is enabled.

When all of the above are true, there is an intermittent window in which:

CheckPermission(document:firstdoc, has_permission, user:caveatedreader) → HAS_PERMISSION (incorrect; should be CONDITIONAL_PERMISSION)

CheckPermission(document:firstdoc, has_permission, user:caveatedreader, context = {"somecondition": 41}) → HAS_PERMISSION (incorrect; should be NO_PERMISSION)

Patches

v1.54.0

Workarounds

Disable the dispatch result cache (ClusterDispatchCacheConfig and DispatchCacheConfig)

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/authzed/spicedb`	≥ 1.34.0&&< 1.54.0	1.54.0`go get github.com/authzed/spicedb@v1.54.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/authzed/spicedb, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/authzed/spicedb to 1.54.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-55866 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### Impact Under concurrency, `CheckPermission` and `CheckBulkPermissions` can return `PERMISSIONSHIP_HAS_PERMISSION` for a (resource, permission, subject) whose correct answer is `PERMISSIONSHIP_CONDITIONAL_PERMISSION`. You are impacted if **all** of the following hold: 1. Your schema has a permission combining relations with an intersection or exclusion, where a subject reaches it through a caveated branch and a non-caveated branch. For example: ```zed definition user {} caveat some_caveat(somecondition int) { somecondition == 42 } definition document { relation reader: