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 — 4 sources updated 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 Sep 16, 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(10)

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

Patch Availability(9)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntuvim-haproxy (3.2.9-1ubuntu2.2) @ resolute2026-09-14ubuntu
redhatrhui5/haproxy-rhel9:17888804562026-09-09redhat
redhathaproxy-0:2.4.17-6.el9_2.52026-08-17redhat
redhathaproxy-0:2.8.14-3.el9_8.22026-08-17redhat
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-0:2.4.22-3.el9_4.32026-08-17redhat
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 ... 3.4.4-1 (102 versions)——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
haproxy3.0.11-1 ... 3.4.4-1 (55 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 14× in last 7d / 78× 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 511 total refreshes for this CVE.

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

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 71.6% 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

See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-55203

Explore →

Is Your Infrastructure Affected by CVE-2026-55203?

EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.

Start Free Scan →Browse All CVEs