Circles' remote-instance signature verification fetches the attacker-supplied keyId URL before...
Summary
SSRF reported (CVE-2026-77164). Confidential information can be exposed externally. Exploitable via POST /apps/circles/event/.
Original description
The description as published by the source.
Circles' remote-instance signature verification fetches the attacker-supplied keyId URL before trust in the remote instance is established, and explicitly allows local/private addresses for this request, bypassing Nextcloud's core SSRF protections. The public, unauthenticated endpoints POST /apps/circles/event/ and POST /apps/circles/incoming/ reach this code path, allowing any unauthenticated user to force the server to issue a GET request to an internal address.
The response body of the internal request is never returned to the requester, so this is blind SSRF: an attacker can determine whether an internal service is reachable, but cannot read its response contents through this endpoint alone.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-77164 has been found.
Attackers can target a specific entry point like POST /apps/circles/event/ over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 6.2/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "CVE-2026-77164" on the vendor's site.
CVE-2026-77164 — CWE-918 / CVSS v3 6.2
Attack vector: local / unauthenticated / no user interaction
Attack surface: POST /apps/circles/event/ / POST /apps/circles/incoming/
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
SSRF (CWE-918) has been reported. Attackers reach the vulnerable code path via POST /apps/circles/event/ without authentication.
Check the vendor advisory for the affected versions. Attack surface: POST /apps/circles/event/ / POST /apps/circles/incoming/.
Severity: Medium (CVSS 6.2/10). Confidential information can be exposed externally.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual POST /apps/circles/event/ requests with malformed payloads or SQL meta-characters. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで影響コンポーネントを特定する。
-
2Hunt for indicators of compromise detect
grep 'POST /apps/circles/event/' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
POST /apps/circles/event/への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。 -
3Post-deployment verification verify
Replay attack against POST /apps/circles/event/ on staging to confirm patch closes the vectorパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番では Step 2 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
References
- web hackerone.com
- web nvd.nist.gov
- web github.com