CVE-2026-55203

CRITICALNVD 9.19.1—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.1 under NVD CVSS v3. EPSS exploit probability: 0.3%, top 72% of all CVEs by exploit prediction. GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
Trending — Patch released this week
9.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.1Exploit: None knownExposed: 0

A fix is available — apply it.

HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer misparse as new FCGI record headers. When contentLength is 65535 and paddingLength is 1 or more, the drl field wraps to 0, causing incorrect record consumption and allowing malicious FastCGI backends to desynchronize the FCGI framing parser, potentially causing request routing errors, response smuggling, or memory safety issues.

CVSS v3
9.1
EG Score
9.1(medium)
EG Risk
41(Track)
EG Risk 41/100SSVC: 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
Severity91% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
28%
KEV
Not listed

Published

June 18, 2026

Last Modified

July 14, 2026

Advisory Details (2)

Auto-updated Aug 1, 2026
Upstream fix merged — awaiting tagged release. Sources: github_commit.
generic

HAProxy - Integer Overflow in FCGI Demux Record Length Field | Advisories | VulnCheck

https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field
github_commit

commit 598527673577 (haproxy/haproxy)

Fix landed in haproxy/haproxy commit 598527673577 — awaiting tagged release

https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd

Vendor Advisories for CVE-2026-55203(9)

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

Patch Availability(8)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuvim-haproxy (2.4.30-0ubuntu0.22.04.2) @ jammy2026-08-21ubuntu
redhathaproxy-0:2.8.14-3.el9_8.22026-08-17redhat
redhathaproxy-0:2.4.17-6.el9_2.52026-08-17redhat
redhathaproxy-0:2.4.22-3.el9_4.32026-08-17redhat
redhathaproxy-0:2.4.22-4.el9_6.32026-08-17redhat
redhathaproxy-0:3.0.5-6.el10_2.22026-08-17redhat
redhathaproxy-0:3.0.5-4.el10_0.32026-08-17redhat
redhathaproxy-main-3.0.25-0.1.hum12026-07-03redhat

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
haproxy2.2.16-1 ... 3.4.3-1 (180 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
haproxy2.6.12-1 ... 3.4.3-1 (100 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
haproxy3.0.11-1 ... 3.4.3-1 (53 versions)——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
haproxy3.0.11-1 ... 3.2.9-1 (31 versions)3.2.20-1—

Weakness Classification(1)

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

Additional Vendor Advisories

(1)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 67× in last 7d / 290× 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 443 total refreshes for this CVE.

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

Related CVEs(same vendor + same CWE)

Frequently asked(5)

What is CVE-2026-55203?
CVE-2026-55203 is a critical vulnerability published on June 18, 2026. HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer misparse as new FCGI record headers. When contentLength is 65535 and paddingLength is 1 or more, the drl field wraps to 0, causing incorrect record…
When was CVE-2026-55203 disclosed?
CVE-2026-55203 was first published in the National Vulnerability Database on June 18, 2026, with the most recent update on July 14, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-55203 actively exploited?
CVE-2026-55203 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 72.0% of all scored CVEs.
What is the CVSS score of CVE-2026-55203?
CVE-2026-55203 has a CVSS v3 base score of 9.1 (NVD).
How do I remediate CVE-2026-55203?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-55203, 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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