Security Digest · Vulnerability record
CVE-2023-48312: Capsule Proxy Authentication bypass using an empty token
capsule-proxy is a reverse proxy for the capsule operator project.
CVSS 9.8 Critical EPSS 0.6% · p47
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.6%, percentile 47: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 47% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
github.com/projectcapsule/capsule-proxy(Go) <= 0.4.5, fixed in 0.4.6;github.com/clastix/capsule-proxy(Go) <= 0.4.5, fixed in 0.4.6. Check your lockfile, including transitive dependencies.
What it is
capsule-proxy is a reverse proxy for the capsule operator project. Affected versions are subject to a privilege escalation vulnerability which is based on a missing check if the user is authenticated based on the TokenReview result. All the clusters running with the anonymous-auth Kubernetes API Server setting disable (set to false) are affected since it would be possible to bypass the token review mechanism, interacting with the upper Kubernetes API Server. This privilege escalation cannot be exploited if you're relying only on client certificates (SSL/TLS). This vulnerability has been addressed in version 0.4.6. Users are advised to upgrade.
From the GitHub advisory
The privilege escalation is based on a missing check if the user is authenticated based on the TokenReview result.
All the clusters running with the anonymous-auth Kubernetes API Server setting disable (set to false) are affected since it would be possible to bypass the token review mechanism, interacting with the upper Kubernetes API Server.
PoC
Start a KinD cluster with the anonymous-auth value to false. If it is true, it uses anonymous permissions which are very limited by default
Install capsule and capsule-proxy
Weakness type: CWE-287.
Product: github.com/projectcapsule/capsule-proxy (Go) · Assigned by: GitHub_M · Published: 2023-11-24
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | github.com/projectcapsule/capsule-proxy | <= 0.4.5 | 0.4.6 |
| Go | github.com/clastix/capsule-proxy | <= 0.4.5 | 0.4.6 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| projectcapsule | capsule-proxy | < 0.4.6 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 9.8 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
| GitHub | 3.1 | 9.8 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
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).
- FIRST EPSS (model of 2026-10-21): 0.57% probability of exploitation activity in the next 30 days; percentile 47.
Timeline
- — CVE record published by GitHub_M
- — GitHub-reviewed advisory GHSA-fpvw-6m5v-hqfp published (critical)
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-fpvw-6m5v-hqfp github.com
- CVE.org record CVE-2023-48312 cve.org
- NVD entry CVE-2023-48312 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- github.com github.com