Vulnerability in github.com/caddyserver/caddy/v2 (CVE-2026-52846)
Summary
Vulnerability in github.com/caddyserver/caddy/v2 (CVE-2026-52846). Risk of unauthorized operations or information disclosure. Exploitable via stripHTML. Mitigation: upgrade to 2.11.4 or later.
Original description
The description as published by the source.
Summary
Caddy’s stripHTML template function cannot reliably remove all HTML tags from input strings. Certain malformed HTML, such as <<>img src=x onerror=alert()>, can bypass the tag-stripping logic, potentially leaving dangerous content in the output if it is later rendered as HTML. This may allow client-side XSS in cases where untrusted strings are rendered unsafely.
Details
The vulnerability originates from funcStripHTML in:
caddy/caddy/caddyhttp/templates/tplcontext.go
func (TemplateContext) funcStripHTML(s string) string {
var buf bytes.Buffer
var inTag, inQuotes bool
var tagStart int
for i, ch := range s {
if inTag {
if ch == '>' && !inQuotes {
inTag = false
} else if ch == '<' && !inQuotes {
// false start
buf.WriteString(s[tagStart:i])
tagStart = i
} else if ch == '"' {
inQuotes = !inQuotes
}
continue
}
if ch == '<' {
inTag = true
tagStart = i
continue
}
buf.WriteRune(ch)
}
if inTag {
// false start
buf.WriteString(s[tagStart:])
}
return buf.String()
}
POC
Caddyfile setup
:8080 {
root * ./site
file_server
templates
}
Templat…
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-2026-52846 has been found in github.com/caddyserver/caddy/v2.
Attackers can target a specific entry point like stripHTML over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 4.2/10.
What to do: upgrade github.com/caddyserver/caddy/v2 to 2.11.4 or later.
If unsure, ask your IT team or search "github.com/caddyserver/caddy/v2 CVE-2026-52846" on the vendor's site.
CVE-2026-52846 (github.com/caddyserver/caddy/v2) — CWE-116 / CVSS v3 4.2
Attack vector: remote (network-reachable) / unauthenticated
Attack surface: stripHTML / funcStripHTML
Patched: 2.11.4 — 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 github.com/caddyserver/caddy/v2. Attackers reach the vulnerable code path via stripHTML without authentication.
Check the vendor advisory for the affected versions of github.com/caddyserver/caddy/v2. Attack surface: stripHTML / funcStripHTML.
Severity: Medium (CVSS 4.2/10). Risk of unauthorized operations or information disclosure.
Update to 2.11.4.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'github.com/caddyserver/caddy/v2' . 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 'github.com/caddyserver/caddy/v2' . | 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
github.com/caddyserver/caddy/v2を grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade github.com/caddyserver/caddy/v2 to 2.11.4ステージング環境で 2.11.4 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を含めること。
-
3Post-deployment verification verify
Confirm patched version is live in production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。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Ubuntu UBUNTU-CVE-2026-52846 caddy
References
- package github.com
- web github.com
- web github.com