SSRF (Server-Side Request Forgery) in lemur (CVE-2026-71303)
Summary
SSRF in lemur (CVE-2026-71303). Confidential information can be exposed externally. Exploitable via PUT /api/1/authorities/. Mitigation: upgrade to 1.9.3 or later.
Original description
The description as published by the source.
Summary
The fix for GHSA-v2wp-frmc-5q3v added _validate_acme_url() to reject acme_url values not in ACME_DIRECTORY_HOST_ALLOWLIST, but the validation is only called at authority creation time (POST). The authority update endpoint (PUT /api/1/authorities/) accepts and stores arbitrary options -- including a modified acme_url -- without invoking the allowlist check. Any user with an authority role (granted by an admin to allow issuing certificates via that authority) can therefore overwrite the stored acme_url with an internal IP or IMDS endpoint. The next certificate issuance via that authority causes Lemur's backend to fetch the attacker-controlled URL, achieving SSRF.
Details
Where the fix lives (POST path -- protected):
lemur/plugins/lemur_acme/plugin.py lines 333-337 (ACMEIssuerPlugin.create_authority):
for option in plugin_options:
if option.get("name") == "certificate":
acme_root = option.get("value")
if option.get("name") == "acme_url":
_validate_acme_url(option.get("value", "")) # allowlist enforced
_validate_acme_url at line 35:
def _validate_acme_url(url):
"""Reject acme_url values that are not in the configured allowlist.
Called at authority creation time only -- existing authorities in the DB
were already trusted when they were created and are not re-validated.
"""
allowed_hosts = current_app.config.get(
"ACME_DIRECTORY_HOST_ALLOWLIST",…
Source: GitHub Security Advisories (Global) 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-2026-71303 has been found in lemur.
Attackers can target a specific entry point like PUT /api/1/authorities/ over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.7/10.
What to do: upgrade lemur to 1.9.3 or later.
If unsure, ask your IT team or search "lemur CVE-2026-71303" on the vendor's site.
CVE-2026-71303 (lemur) — CWE-918 / CVSS v3 7.7
Attack vector: remote (network-reachable) / no user interaction
Attack surface: PUT /api/1/authorities/ / POST /api/1/auth/login / GET /api/1/auth/me / PUT /api/1/authorities/1
Patched: 1.9.3 — apply immediately
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) exists in lemur. Attackers reach the vulnerable code path via PUT /api/1/authorities/.
Check the vendor advisory for the affected versions of lemur. Attack surface: PUT /api/1/authorities/ / POST /api/1/auth/login / GET /api/1/auth/me / PUT /api/1/authorities/1.
Severity: High (CVSS 7.7/10). Confidential information can be exposed externally.
Update to 1.9.3.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual PUT /api/1/authorities/ requests with malformed payloads or SQL meta-characters. Run grep -r 'lemur' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'lemur' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
lemurを grep し、稼働しているサービス・バージョンを把握する。 -
2Hunt for indicators of compromise detect
grep 'PUT /api/1/authorities/' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
PUT /api/1/authorities/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。 -
3Apply patch patch
Upgrade lemur to 1.9.3ステージング環境で 1.9.3 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスと、Step 2 で見つけた異常検知の続報チェックを含めること。
-
4Post-deployment verification verify
Replay attack against PUT /api/1/authorities/ 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
- advisory github.com
- advisory nvd.nist.gov
- package github.com
- package pypi.org
- web github.com
- web github.com
- web github.com