Vulnerability in haproxy (CVE-2026-55204)
Summary
Vulnerability in haproxy (CVE-2026-55204). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 3.4.1 or later.
Original description
The description as published by the source.
HAProxy through 3.4.0, fixed in commit 9a6d1fe, contains a null pointer dereference vulnerability in hpack_dht_insert() within src/hpack-tbl.c that fails to validate the return value of hpack_dht_defrag() when the memory pool is exhausted. An attacker can trigger HPACK dynamic table insertions under memory pressure to dereference a NULL pointer and crash HAProxy worker processes, causing denial of service.
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-2026-55204 has been found in haproxy.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade haproxy to 3.4.1 or later.
If unsure, ask your IT team or search "haproxy CVE-2026-55204" on the vendor's site.
CVE-2026-55204 (haproxy) — CWE-476 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 3.4.1 — 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-476) exists in haproxy.
Check the vendor advisory for the affected versions of haproxy.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 3.4.1.
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 'haproxy' . 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
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1Identify exposure identify
grep -r 'haproxy' . | 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
haproxy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 haproxy to 3.4.1ステージング環境で 3.4.1 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
- Debian DEBIAN-CVE-2026-55204 haproxy
- Ubuntu UBUNTU-CVE-2026-55204 haproxy
References
- advisory vulncheck.com
- patch github.com
- web nvd.nist.gov
- web github.com