CVE-2021-40346

HIGHNVD 7.58.3▲
EchelonGraph scoreHIGH confidence

Score elevated to 8.3 because EPSS predicts 58% probability of exploitation within the next 30 days (top 1.0% of all CVEs). NVD baseline CVSS 7.5 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, nvd
Elevated
8.3EG
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 58%
CISA-KEV: Not listedEPSS PROB: 58%CVSS: 7.5Exploit: Elevated riskExposed: 0

A fix is available — apply it.

An integer overflow exists in HAProxy 2.0 through 2.5 in htx_add_header that can be exploited to perform an HTTP request smuggling attack, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.

CVSS v3
7.5
EG Score
8.3(high)
EG Risk
65(Track)
EG Risk 65/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity83% × 45%
Exploitation58% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
58%
EPSS %ILE
99%
KEV
Not listed

Published

September 8, 2021

Last Modified

November 21, 2024

References (20)

Patch Availability(5)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuvim-haproxy (2.2.9-1ubuntu0.2) @ hirsute2026-05-26ubuntu
redhathaproxy-0:2.0.19-2.el72022-01-19redhat
redhathaproxy-0:2.0.16-2.el72022-01-12redhat
redhathaproxy-0:2.2.13-2.el72022-01-05redhat
redhathaproxy-0:2.2.15-2.el82021-11-10redhat

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
haproxy2.2.9-2, 2.2.9-2+deb11u1, 2.2.9-2+deb11u1~bpo10+1, 2.2.9-2+deb11u2~bpo10+12.2.9-2+deb11u2—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
haproxy—2.2.16-3—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
haproxy—2.2.16-3—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
haproxy—2.2.16-3—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

All Vendor Advisories

(5)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 6× in last 7d / 24× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 116 total refreshes for this CVE.

  1. 2026-09-19 15:38 UTCEPSS rescore
  2. 2026-09-18 19:23 UTCEPSS rescore
  3. 2026-09-17 19:23 UTCEPSS rescore
  4. 2026-09-17 19:23 UTCEPSS rescore
  5. 2026-09-16 14:05 UTCEPSS rescore
  6. 2026-09-15 03:06 UTCEPSS rescore
  7. 2026-09-12 14:57 UTCEPSS rescore
  8. 2026-09-11 14:49 UTCEPSS rescore
  9. 2026-09-11 09:33 UTCEPSS rescore
  10. 2026-09-08 21:56 UTCEPSS rescore
  11. 2026-09-06 13:45 UTCEPSS rescore
  12. 2026-09-06 08:30 UTCOSV refresh
  13. 2026-09-05 15:25 UTCEPSS rescore
  14. 2026-09-04 13:57 UTCEPSS rescore
  15. 2026-09-02 14:09 UTCEPSS rescore
  16. 2026-09-01 13:50 UTCEPSS rescore
  17. 2026-09-01 03:33 UTCEPSS rescore
  18. 2026-08-30 19:14 UTCEPSS rescore
  19. 2026-08-30 19:14 UTCEPSS rescore
  20. 2026-08-30 01:19 UTCEPSS rescore
  21. 2026-08-28 21:37 UTCEPSS rescore
  22. 2026-08-26 14:43 UTCEPSS rescore
  23. 2026-08-25 13:46 UTCEPSS rescore
  24. 2026-08-24 14:13 UTCEPSS rescore
  25. 2026-08-21 23:46 UTCEPSS rescore
Show 75 more
  1. 2026-08-20 22:52 UTCEPSS rescore
  2. 2026-08-20 22:52 UTCEPSS rescore
  3. 2026-08-19 19:04 UTCOSV refresh
  4. 2026-08-19 17:01 UTCEPSS rescore
  5. 2026-08-18 13:45 UTCEPSS rescore
  6. 2026-08-17 13:44 UTCEPSS rescore
  7. 2026-08-16 02:11 UTCEPSS rescore
  8. 2026-08-15 01:27 UTCEPSS rescore
  9. 2026-08-13 21:57 UTCEPSS rescore
  10. 2026-08-12 13:48 UTCEPSS rescore
  11. 2026-08-11 13:38 UTCEPSS rescore
  12. 2026-08-08 16:33 UTCEPSS rescore
  13. 2026-08-07 16:24 UTCEPSS rescore
  14. 2026-08-05 19:14 UTCEPSS rescore
  15. 2026-08-04 14:59 UTCOSV refresh
  16. 2026-07-30 16:25 UTCEPSS rescore
  17. 2026-07-30 01:28 UTCEPSS rescore
  18. 2026-07-28 15:33 UTCEPSS rescore
  19. 2026-07-26 14:52 UTCEPSS rescore
  20. 2026-07-26 14:52 UTCEPSS rescore
  21. 2026-07-25 14:15 UTCEPSS rescore
  22. 2026-07-24 14:15 UTCEPSS rescore
  23. 2026-07-23 14:16 UTCEPSS rescore
  24. 2026-07-23 02:04 UTCEG score recompute▲ 0.80
  25. 2026-07-22 22:50 UTCEG score recompute▼ 1.50
  26. 2026-07-22 14:06 UTCEPSS rescore
  27. 2026-07-21 15:22 UTCEPSS rescore
  28. 2026-07-21 15:22 UTCEPSS rescore
  29. 2026-07-20 17:05 UTCEPSS rescore
  30. 2026-07-19 02:27 UTCEPSS rescore
  31. 2026-07-18 12:29 UTCOSV refresh
  32. 2026-07-18 10:02 UTCEPSS rescore
  33. 2026-07-18 10:02 UTCEPSS rescore
  34. 2026-07-16 17:00 UTCEPSS rescore
  35. 2026-07-16 17:00 UTCEPSS rescore
  36. 2026-07-15 16:55 UTCEPSS rescore
  37. 2026-07-15 16:55 UTCEPSS rescore
  38. 2026-07-13 22:27 UTCEPSS rescore
  39. 2026-07-13 22:27 UTCEPSS rescore
  40. 2026-07-13 06:11 UTCEPSS rescore
  41. 2026-07-13 06:11 UTCEPSS rescore
  42. 2026-07-12 05:44 UTCEPSS rescore
  43. 2026-07-11 08:25 UTCEPSS rescore
  44. 2026-07-11 08:25 UTCEPSS rescore
  45. 2026-07-09 19:07 UTCEPSS rescore
  46. 2026-07-07 13:43 UTCEPSS rescore
  47. 2026-07-05 02:28 UTCEPSS rescore
  48. 2026-07-05 02:28 UTCEPSS rescore
  49. 2026-07-02 16:57 UTCEPSS rescore
  50. 2026-07-01 15:04 UTCEPSS rescore
  51. 2026-06-30 15:30 UTCOSV refresh
  52. 2026-06-28 14:05 UTCEPSS rescore
  53. 2026-06-27 03:06 UTCEPSS rescore
  54. 2026-06-27 03:06 UTCEPSS rescore
  55. 2026-06-25 13:48 UTCEPSS rescore
  56. 2026-06-25 13:48 UTCEPSS rescore
  57. 2026-06-24 14:03 UTCEPSS rescore
  58. 2026-06-24 14:03 UTCEPSS rescore
  59. 2026-06-23 21:31 UTCEPSS rescore
  60. 2026-06-23 21:31 UTCEPSS rescore
  61. 2026-06-21 01:58 UTCEPSS rescore
  62. 2026-06-21 01:58 UTCEPSS rescore
  63. 2026-06-17 17:51 UTCEPSS rescore
  64. 2026-06-17 17:51 UTCEPSS rescore
  65. 2026-06-17 17:51 UTCEPSS rescore
  66. 2026-06-16 17:51 UTCEPSS rescore
  67. 2026-06-16 17:51 UTCEPSS rescore
  68. 2026-06-15 17:46 UTCEPSS rescore
  69. 2026-06-12 23:10 UTCEPSS rescore
  70. 2026-06-12 22:10 UTCOSV refresh
  71. 2026-06-11 13:58 UTCEPSS rescore
  72. 2026-06-11 13:58 UTCEPSS rescore
  73. 2026-06-05 22:45 UTCEPSS rescore
  74. 2026-06-05 06:09 UTCEPSS rescore
  75. 2026-06-05 06:09 UTCEPSS rescore

Publicly available exploits

(4 references)

Working exploit code is in the public domain (4 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCVulnmachines/HAProxy_CVE-2021-40346
    First seen Nov 8, 2021

    HAProxy CVE-2021-40346

    Open source ↗
  • GitHub PoCdonky16/CVE-2021-40346-POC
    First seen Sep 10, 2021

    CVE-2021-40346 integer overflow enables http smuggling

    Open source ↗
  • GitHub PoCalikarimi999/CVE-2021-40346
    First seen Sep 10, 2021
    Open source ↗
  • GitHub PoCknqyf263/CVE-2021-40346
    First seen Sep 8, 2021

    CVE-2021-40346 PoC (HAProxy HTTP Smuggling)

    Open source ↗

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2021-40346?
CVE-2021-40346 is a high vulnerability published on September 8, 2021. An integer overflow exists in HAProxy 2.0 through 2.5 in htxaddheader that can be exploited to perform an HTTP request smuggling attack, allowing an attacker to bypass all configured http-request HAProxy ACLs and possibly other ACLs.
When was CVE-2021-40346 disclosed?
CVE-2021-40346 was first published in the National Vulnerability Database on September 8, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-40346 actively exploited?
CVE-2021-40346 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 58% probability of exploitation in the next 30 days, which ranks it in the top 1.0% of all scored CVEs.
What is the CVSS score of CVE-2021-40346?
CVE-2021-40346 has a CVSS v3 base score of 7.5 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.3.
How do I remediate CVE-2021-40346?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-40346, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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