CVE-2026-55203

CRITICALNVD 9.19.1
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This critical-severity CVE scores 9.1 under NVD CVSS v3. EPSS exploit probability: 0.3% (26th percentile of EPSS-scored CVEs). GitHub Security Advisory CVSS 7.5 is lower than this score; a lower GitHub score revises it only when its advisory is newer than the CVE record's last change, and this advisory (published 2026-06-18) is not newer than that change (2026-10-26), so it does not.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — 4 sources updated this week

Also known asEUVD-2026-37905 (ENISA EUVD) · GHSA-58mj-cmhg-35rg (GitHub Security Advisories)Source: ENISA EUVD

9.1EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.3%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 impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity91% × 45%
Impact severity (EG Severity): CVSS 9.1 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.3% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
26th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (9.1): severity, escalated by confirmed exploitation. This CVE's 9.1 is its impact severity (EG Severity), not escalated.

EG Severity
9.1 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.NVD CVSS v3 · CVSS v3.0 or v3.1
EG Likelihood
0.3% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-01). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

June 18, 2026

Last Modified

October 26, 2026

Advisory Details (2)

Auto-updated Sep 16, 2026
Patch available. Sources: github_commit.
Web page

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) @ resolute2026-11-01ubuntu
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 31× in last 7d / 107× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 628 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 528 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-02 08:23 UTCEG score recompute
  2. 2026-11-02 08:23 UTCVendor advisory
  3. 2026-11-02 08:23 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  4. 2026-11-01 16:34 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  5. 2026-11-01 09:09 UTCEG score recompute
  6. 2026-11-01 09:09 UTCVendor advisory
  7. 2026-11-01 09:09 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  8. 2026-10-31 16:33 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  9. 2026-10-31 09:55 UTCEG score recompute
  10. 2026-10-31 09:55 UTCVendor advisory
  11. 2026-10-31 09:55 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  12. 2026-10-30 16:34 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  13. 2026-10-30 10:41 UTCEG score recompute
  14. 2026-10-30 10:41 UTCVendor advisory
  15. 2026-10-30 10:41 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  16. 2026-10-29 16:33 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  17. 2026-10-29 11:27 UTCEG score recompute
  18. 2026-10-29 11:27 UTCVendor advisory
  19. 2026-10-29 11:27 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  20. 2026-10-28 16:32 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  21. 2026-10-28 12:13 UTCEG score recompute
  22. 2026-10-28 12:13 UTCVendor advisory
  23. 2026-10-28 12:13 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  24. 2026-10-27 16:32 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  25. 2026-10-27 12:59 UTCVendor advisory
Show 75 more
  1. 2026-10-27 12:58 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  2. 2026-10-27 12:58 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  3. 2026-10-27 03:55 UTCEG score recompute
  4. 2026-10-27 03:55 UTCVendor advisory
  5. 2026-10-27 03:55 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  6. 2026-10-26 16:31 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  7. 2026-10-26 00:26 UTCEG score recompute
  8. 2026-10-26 00:26 UTCVendor advisory
  9. 2026-10-26 00:26 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  10. 2026-10-25 16:33 UTCEPSS rescoreEPSS 0.3% · 26th percentile
  11. 2026-10-25 14:19 UTCEG score recompute
  12. 2026-10-25 03:44 UTCEG score recompute
  13. 2026-10-25 03:44 UTCVendor advisory
  14. 2026-10-25 03:44 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  15. 2026-10-24 16:33 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  16. 2026-10-24 04:30 UTCEG score recompute
  17. 2026-10-24 04:30 UTCVendor advisory
  18. 2026-10-24 04:30 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  19. 2026-10-23 16:32 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  20. 2026-10-23 05:16 UTCEG score recompute
  21. 2026-10-23 05:16 UTCVendor advisory
  22. 2026-10-23 05:16 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  23. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  24. 2026-10-22 06:01 UTCEG score recompute
  25. 2026-10-22 06:01 UTCVendor advisory
  26. 2026-10-22 06:00 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  27. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  28. 2026-10-21 06:43 UTCEG score recompute
  29. 2026-10-21 06:43 UTCVendor advisory
  30. 2026-10-21 06:43 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  31. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  32. 2026-10-20 07:29 UTCEG score recompute
  33. 2026-10-20 07:29 UTCVendor advisory
  34. 2026-10-20 07:28 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  35. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  36. 2026-10-19 08:14 UTCEG score recompute
  37. 2026-10-19 08:14 UTCVendor advisory
  38. 2026-10-19 08:13 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  39. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  40. 2026-10-18 08:59 UTCVendor advisory
  41. 2026-10-18 08:59 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  42. 2026-10-18 03:30 UTCEG score recompute
  43. 2026-10-17 16:34 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  44. 2026-10-17 06:38 UTCEG score recompute
  45. 2026-10-17 06:38 UTCVendor advisory
  46. 2026-10-17 06:38 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  47. 2026-10-16 16:42 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  48. 2026-10-16 07:22 UTCEG score recompute
  49. 2026-10-16 07:22 UTCVendor advisory
  50. 2026-10-16 07:21 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  51. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  52. 2026-10-15 06:17 UTCEG score recompute
  53. 2026-10-15 06:17 UTCVendor advisory
  54. 2026-10-15 06:17 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  55. 2026-10-14 16:33 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  56. 2026-10-14 01:56 UTCEG score recompute
  57. 2026-10-14 01:56 UTCVendor advisory
  58. 2026-10-14 01:56 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  59. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  60. 2026-10-12 22:13 UTCEG score recompute
  61. 2026-10-12 22:13 UTCVendor advisory
  62. 2026-10-12 22:12 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  63. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  64. 2026-10-12 15:56 UTCEG score recompute
  65. 2026-10-12 06:54 UTCVendor advisory
  66. 2026-10-12 06:53 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5
  67. 2026-10-11 19:39 UTCEG score recompute
  68. 2026-10-11 16:54 UTCEG score recompute
  69. 2026-10-11 14:17 UTCEG score recompute
  70. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  71. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  72. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  73. 2026-10-08 17:28 UTCEG score recompute
  74. 2026-10-08 17:28 UTCVendor advisory
  75. 2026-10-08 17:28 UTCGHSA enrichmentGHSA-58mj-cmhg-35rg · GitHub severity CRITICAL · GitHub CVSS 7.5

Related CVEs(same product + same vendor + same CWE)

Frequently asked(5)

What is CVE-2026-55203?
CVE-2026-55203 is a critical-severity vulnerability; its CVE record was 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 made public?
CVE-2026-55203 was made public on June 16, 2026: that is the date its CVE record's CNA, VulnCheck, gives for when the vulnerability was made public. The CVE record itself was published on June 18, 2026. EchelonGraph's copy of the record carries a last-modified date of October 26, 2026; the record at its source may have been updated since.
Is CVE-2026-55203 actively exploited?
CVE-2026-55203 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (26th 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.

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