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
9.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.6%CVSS: 9.1Exploit: None knownExposed services: Not assessed

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
9.1CRITICALmedium confidence
EG Risk
41
EG Risk 41/100

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%
EPSS PROB
0.6%
EPSS %ILE
45th
KEV
Not listed

Published

June 18, 2026

Last Modified

July 14, 2026

Advisory Details (2)

Auto-updated Sep 16, 2026
Patch available. 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 / EcosystemFix (by version range) / 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 rangeFix by version rangeDependents
haproxy2.2.16-1 ... 3.4.3-1 (180 versions)
  • every version on: no fix on record
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
haproxy2.6.12-1 ... 3.4.6-1 (105 versions)
  • every version on: no fix on record
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
haproxy3.0.11-1 ... 3.4.6-1 (58 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
haproxy3.0.11-1 ... 3.2.9-1 (31 versions)
  • every version up to 3.2.20-1: fixed in 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 7× in last 7d / 32× 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 524 total refreshes for this CVE.

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

Related CVEs(same product + 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 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 0.6% probability of exploitation in the next 30 days (45th percentile of EPSS-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?
A fix for CVE-2026-55203 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-55203 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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