Vulnerability in YAFNET.Core (CVE-2026-43938)
Summary
Vulnerability in YAFNET.Core (CVE-2026-43938). Confidential information can be exposed externally. Exploitable via GET /api/Attachments/GetAttachment. Mitigation: upgrade to 3.2.12 or later.
Original description
The description as published by the source.
Description:
Stored (second-order) Cross-Site Scripting (XSS) occurs when attacker-controlled input is persisted through one component of an application and later rendered, without proper sanitization or contextual output encoding, by a completely different component — often one that implicitly trusts the stored data. Because the dangerous sink is typically a privileged administrative interface, the payload executes in the browser of a high-value user (such as an administrator) and inherits their authenticated session. This class of issue is especially severe when the entry point is an HTTP header on an unauthenticated endpoint, since the attack surface extends to any anonymous attacker on the internet with no prerequisites.
Issue Details:
The application's database logger (YAFNET.Core/Logger/DbLogger.cs) captures the incoming request's User-Agent header into a JObject, serializes it with JsonConvert, and stores the result in the EventLog.Description column whenever an event (e.g., an unhandled exception) is logged. The admin event-log page (YetAnotherForum.NET/Pages/Admin/EventLog.cshtml.cs) later deserializes that JSON in FormatStackTrace() and interpolates the UserAgent value directly into an HTML string with no encoding, and the Razor view EventLog.cshtml emits the result through @Html.Raw. Critically, the attacker does not need to be authenticated: the unauthenticated endpoint GET /api/Attachments/GetAttachment?attachmentId=2147483647 relia…
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-2026-43938 has been found in YAFNET.Core.
Attackers can target a specific entry point like GET /api/Attachments/GetAttachment over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.1/10.
What to do: upgrade YAFNET.Core to 3.2.12 or later.
If unsure, ask your IT team or search "YAFNET.Core CVE-2026-43938" on the vendor's site.
CVE-2026-43938 (YAFNET.Core) — CWE-116 / CVSS v3 8.1
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: GET /api/Attachments/GetAttachment / JObject / JsonConvert / EventLog.Description
Patched: 3.2.12 — 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.
A vulnerability (CWE-116) exists in YAFNET.Core. Attackers reach the vulnerable code path via GET /api/Attachments/GetAttachment without authentication.
Check the vendor advisory for the affected versions of YAFNET.Core. Attack surface: GET /api/Attachments/GetAttachment / JObject / JsonConvert / EventLog.Description.
Severity: High (CVSS 8.1/10). Confidential information can be exposed externally.
Update to 3.2.12.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual GET /api/Attachments/GetAttachment requests with malformed payloads or SQL meta-characters. Run grep -r 'YAFNET.Core' . 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 'YAFNET.Core' . | 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
YAFNET.Core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 'GET /api/Attachments/GetAttachment' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'アクセスログで
GET /api/Attachments/GetAttachment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 YAFNET.Core to 3.2.12ステージング環境で 3.2.12 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 GET /api/Attachments/GetAttachment 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 nvd.nist.gov
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com