CVE-2026-32301: Centrifugo: SSRF via unverified JWT claims interpolated into dynamic JWKS endpoint URL

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.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.4%, percentile 30: FIRST’s model estimates a 0.4% chance of exploitation activity in the next 30 days, higher than 30% 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/centrifugal/centrifugo/v6 (Go) <= 6.6.2, fixed in 6.7.0; github.com/centrifugal/centrifugo (Go) <= 2.4.0, no fixed version listed; github.com/centrifugal/centrifugo/v3 (Go) <= 3.2.3, no fixed version listed; github.com/centrifugal/centrifugo/v4 (Go) <= 4.1.5, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

Centrifugo is an open-source scalable real-time messaging server. Prior to 6.7.0, Centrifugo is vulnerable to Server-Side Request Forgery (SSRF) when configured with a dynamic JWKS endpoint URL using template variables (e.g. {{tenant}}). An unauthenticated attacker can craft a JWT with a malicious iss or aud claim value that gets interpolated into the JWKS fetch URL before the token signature is verified, causing Centrifugo to make an outbound HTTP request to an attacker-controlled destination. This vulnerability is fixed in 6.7.0.

From the GitHub advisory

Summary Centrifugo is vulnerable to Server-Side Request Forgery (SSRF) when configured with a dynamic JWKS endpoint URL using template variables (e.g. {{tenant}}). An unauthenticated attacker can craft a JWT with a malicious iss or aud claim value that gets interpolated into the JWKS fetch URL before the token signature is verified, causing Centrifugo to make an outbound HTTP request to an attacker-controlled destination.

Details In internal/jwtverify/tokenverifierjwt.go, the functions VerifyConnectToken and VerifySubscribeToken follow this flawed order of operations: 1. Token is parsed without verification: jwt.ParseNoVerify([]byte(t)) 2. Claims are decoded from the unverified token 3. validateClaims() runs — extracting named regex capture groups from issuerregex/audienceregex into tokenVars map using attacker-controlled iss/aud claim values 4. verifySignatureByJWK(token, tokenVars) is called — passing attacker-controlled tokenVars to the JWKS manager 5. In internal/jwks/manager.go, fetchKey() interpolates tokenVars directly into the JWKS URL: jwkURL := m.url.ExecuteString(tokenVars) 6. Centrifugo makes an HTTP GET request to the attacker-controlled URL

Suppressed the security linter on this line with an incorrect comment: //nolint:gosec // URL is from server configuration, not user input. The URL is NOT purely from server configuration — it is partially constructed from unverified user-supplied JWT claims.

Signature verification happens too late — after the SSRF has already fired.

PoC Required config (config.json):

Weakness type: CWE-918.

Product: github.com/centrifugal/centrifugo/v6 (Go) · Assigned by: GitHub_M · Published: 2026-03-12

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• 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 yes, technical impact partial.
• FIRST EPSS (model of 2026-10-21): 0.37% probability of exploitation activity in the next 30 days; percentile 30.

Timeline

• 2026-03-12 — CVE record published by GitHub_M
• 2026-03-13 — CVE record last updated
• 2026-03-13 — GitHub-reviewed advisory GHSA-j77h-rr39-c552 published (critical)

Sources and references

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

Vulnerability records

1. GitHub Advisory GHSA-j77h-rr39-c552 github.com
2. CVE.org record CVE-2026-32301 cve.org
3. NVD entry CVE-2026-32301 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. pkg.go.dev pkg.go.dev

Critical Go advisories · Today’s Security Digest