CVE-2026-77463

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CVE-2026-77463

Summary: Remark42: Rate limit bypass via unconditional trust of X-Forwarded-For/X-Real-IP headers in direct-internet deployment

Details: Remark42 is a self-hosted comment engine for blogs, articles, or any other place where readers can add comments. From 1.0.0 until 1.16.2, Remark42 globally trusts True-Client-IP, X-Real-IP, and X-Forwarded-For without verifying that the direct peer is a trusted proxy, and middleware.RealIP overwrites r.RemoteAddr before per-IP controls run. In a directly reachable deployment, or a proxy that forwards attacker-controlled headers, a remote attacker can rotate spoofed forwarding headers to obtain fresh token buckets for rate-limited endpoints, bypass vote de-duplication when --votes-ip is enabled, mint anonymous identities, and poison stored comment IPs and request logs. The global concurrent-request throttle and per-request timeouts still limit availability impact. Mitigation support is available in version 1.16.2, but operators must configure --trusted-proxy for the deployment topology.

References: https://github.com/umputun/remark42/releases/tag/backend/v1.16.2, https://remark42.com/docs/configuration/parameters/#trusted-proxies-and-client-ip, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/77xxx/CVE-2026-77463.json, https://github.com/umputun/remark42/security/advisories/GHSA-56x6-q882-mf27, https://nvd.nist.gov/vuln/detail/CVE-2026-77463, https://github.com/umputun/remark42/commit/b1502801facd7782a1c70fd51f8ad5c2eb650d39, https://github.com/umputun/remark42/commit/e62b3c830d81659cf5d2687b0c8261da7d42fdab, https://github.com/umputun/remark42/pull/2116, https://github.com/umputun/remark42/pull/2118