CVE-2026-33555

MEDIUMNVD 5.84.0▼
EchelonGraph scoreMEDIUM confidence

Score 4.0 from GitHub Security Advisory published 2026-04-13. NVD baseline CVSS 4.0; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
Elevated
5.8
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 5.8Exploit: NoneExposed: 0

A fix is available — apply it.

An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.

CVSS v3
5.8
EG Score
4.0(medium)
EG Risk
—
EPSS
21.8%
KEV
Not listed

Published

April 13, 2026

Last Modified

June 29, 2026

Advisory Details (5)

Auto-updated Jun 29, 2026
Upstream fix merged — awaiting tagged release. Sources: github_commit.
generic

HAProxy HTTP/3 -> HTTP/1 Desync: Cross-Protocol Smuggling via a Standalone QUIC FIN (CVE-2026-33555) | CyberSec Notes

https://r3verii.github.io/cve/2026/04/14/haproxy-h3-standalone-fin-smuggling.html
generic

[ANNOUNCE] haproxy-3.3.6

https://www.mail-archive.com/haproxy@formilux.org/msg46752.html
generic

HAProxy - The Reliable, High Perf. TCP/HTTP Load Balancer

https://www.haproxy.org
generic

Changelog | HAProxy ALOHA

https://www.haproxy.com/documentation/haproxy-aloha/changelog/
github_commit

commit 05a295441c62 (haproxy/haproxy)

Fix landed in haproxy/haproxy commit 05a295441c62 — awaiting tagged release

https://github.com/haproxy/haproxy/commit/05a295441c621089ffa4318daf0dbca2dd756a84

Vendor Advisories for CVE-2026-33555(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
redhathaproxy-main-3.0.19-1.1.hum12026-04-17redhat

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.

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 8× in last 7d / 39× 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 114 total refreshes for this CVE.

  1. 2026-07-22 14:08 UTCEPSS rescore
  2. 2026-07-21 15:24 UTCEPSS rescore
  3. 2026-07-20 17:08 UTCEPSS rescore
  4. 2026-07-20 12:02 UTCOSV refresh
  5. 2026-07-19 14:31 UTCEPSS rescore
  6. 2026-07-19 02:29 UTCEPSS rescore
  7. 2026-07-18 10:04 UTCEPSS rescore
  8. 2026-07-16 17:03 UTCEPSS rescore
  9. 2026-07-15 16:57 UTCEPSS rescore
  10. 2026-07-15 16:57 UTCEPSS rescore
  11. 2026-07-15 02:00 UTCEPSS rescore
  12. 2026-07-13 22:30 UTCEPSS rescore
  13. 2026-07-13 06:13 UTCEPSS rescore
  14. 2026-07-13 06:13 UTCEPSS rescore
  15. 2026-07-12 05:46 UTCEPSS rescore
  16. 2026-07-11 08:27 UTCEPSS rescore
  17. 2026-07-09 19:10 UTCEPSS rescore
  18. 2026-07-07 13:46 UTCEPSS rescore
  19. 2026-07-06 16:27 UTCEPSS rescore
  20. 2026-07-06 16:27 UTCEPSS rescore
  21. 2026-07-06 02:23 UTCEPSS rescore
  22. 2026-07-06 02:23 UTCEPSS rescore
  23. 2026-07-05 02:30 UTCEPSS rescore
  24. 2026-07-04 06:31 UTCEPSS rescore
  25. 2026-07-01 15:06 UTCEPSS rescore
Show 75 more
  1. 2026-06-30 23:22 UTCEPSS rescore
  2. 2026-06-29 16:05 UTCNVD updateCVSS v3 → 5.8
  3. 2026-06-29 14:06 UTCEPSS rescore
  4. 2026-06-29 14:06 UTCEPSS rescore
  5. 2026-06-28 14:07 UTCEPSS rescore
  6. 2026-06-28 14:07 UTCEPSS rescore
  7. 2026-06-28 04:56 UTCEPSS rescore
  8. 2026-06-28 04:56 UTCEPSS rescore
  9. 2026-06-27 03:08 UTCEPSS rescore
  10. 2026-06-25 13:49 UTCEPSS rescore
  11. 2026-06-25 13:49 UTCEPSS rescore
  12. 2026-06-24 14:05 UTCEPSS rescore
  13. 2026-06-23 21:33 UTCEPSS rescore
  14. 2026-06-23 21:33 UTCEPSS rescore
  15. 2026-06-22 14:25 UTCEPSS rescore
  16. 2026-06-22 14:25 UTCEPSS rescore
  17. 2026-06-21 14:56 UTCEPSS rescore
  18. 2026-06-21 14:56 UTCEPSS rescore
  19. 2026-06-21 01:59 UTCEPSS rescore
  20. 2026-06-19 19:25 UTCEPSS rescore
  21. 2026-06-19 19:25 UTCEPSS rescore
  22. 2026-06-18 17:52 UTCEPSS rescore
  23. 2026-06-18 17:52 UTCEPSS rescore
  24. 2026-06-17 17:53 UTCEPSS rescore
  25. 2026-06-16 17:52 UTCEPSS rescore
  26. 2026-06-15 17:49 UTCEPSS rescore
  27. 2026-06-14 23:18 UTCEPSS rescore
  28. 2026-06-14 21:44 UTCVendor advisory
  29. 2026-06-14 21:44 UTCGHSA enrichment
  30. 2026-06-13 23:00 UTCEPSS rescore
  31. 2026-06-12 23:12 UTCEPSS rescore
  32. 2026-06-12 23:12 UTCEPSS rescore
  33. 2026-06-11 19:37 UTCVendor advisory
  34. 2026-06-11 19:37 UTCGHSA enrichment
  35. 2026-06-11 14:00 UTCEPSS rescore
  36. 2026-06-10 22:18 UTCEPSS rescore
  37. 2026-06-10 13:22 UTCEPSS rescore
  38. 2026-06-10 11:29 UTCVendor advisory
  39. 2026-06-10 11:29 UTCGHSA enrichment
  40. 2026-06-09 11:15 UTCVendor advisory
  41. 2026-06-09 11:15 UTCGHSA enrichment
  42. 2026-06-08 14:17 UTCEPSS rescore
  43. 2026-06-08 14:17 UTCEPSS rescore
  44. 2026-06-08 07:39 UTCVendor advisory
  45. 2026-06-08 07:39 UTCGHSA enrichment
  46. 2026-06-07 15:25 UTCEPSS rescore
  47. 2026-06-07 15:25 UTCEPSS rescore
  48. 2026-06-07 15:25 UTCEPSS rescore
  49. 2026-06-07 07:21 UTCVendor advisory
  50. 2026-06-07 07:21 UTCGHSA enrichment
  51. 2026-06-06 13:47 UTCEPSS rescore
  52. 2026-06-06 13:47 UTCEPSS rescore
  53. 2026-06-05 22:47 UTCEPSS rescore
  54. 2026-06-05 22:47 UTCEPSS rescore
  55. 2026-06-05 06:10 UTCEPSS rescore
  56. 2026-06-05 06:10 UTCEPSS rescore
  57. 2026-06-04 13:12 UTCEPSS rescore
  58. 2026-06-04 13:12 UTCEPSS rescore
  59. 2026-06-02 21:41 UTCVendor advisory
  60. 2026-06-02 21:41 UTCGHSA enrichment
  61. 2026-06-02 20:13 UTCEPSS rescore
  62. 2026-06-01 21:15 UTCVendor advisory
  63. 2026-06-01 21:15 UTCGHSA enrichment
  64. 2026-06-01 13:52 UTCEPSS rescore
  65. 2026-06-01 13:52 UTCEPSS rescore
  66. 2026-06-01 13:51 UTCEPSS rescore
  67. 2026-05-31 22:30 UTCEPSS rescore
  68. 2026-05-31 22:30 UTCEPSS rescore
  69. 2026-05-31 00:16 UTCEPSS rescore
  70. 2026-05-31 00:16 UTCEPSS rescore
  71. 2026-05-31 00:16 UTCEPSS rescore
  72. 2026-05-29 13:44 UTCEPSS rescore
  73. 2026-05-29 13:44 UTCEPSS rescore
  74. 2026-05-28 13:44 UTCEPSS rescore
  75. 2026-05-28 13:44 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-33555?
CVE-2026-33555 is a medium vulnerability published on April 13, 2026. An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be…
When was CVE-2026-33555 disclosed?
CVE-2026-33555 was first published in the National Vulnerability Database on April 13, 2026, with the most recent update on June 29, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-33555 actively exploited?
CVE-2026-33555 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 21.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-33555?
CVE-2026-33555 has a CVSS v3 base score of 5.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 4.0.
How do I remediate CVE-2026-33555?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-33555, 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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