CVE-2026-34831

MEDIUMNVD 4.84.8—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 4.8 under NVD CVSS v3. EPSS exploit probability: 0.0%, top 86% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
4.8
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS: 0%CVSS: 4.8Exploit: NoneExposed: 0

A fix is available — apply it.

Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.

CVSS v3
4.8
EG Score
4.8(medium)
EPSS
4.4%
KEV
Not listed

Published

April 2, 2026

Last Modified

April 16, 2026

References (1)

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
ubunturuby-rack (3.1.16-0.1ubuntu0.3) @ questing2026-06-11ubuntu

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

(1 across 1 ecosystem)
RubyGems(1)
PackageVulnerable rangeFixed inDependents
rack3.2.0 ... 3.2.5 (6 versions)3.2.6—

Weakness Classification(2)

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

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

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.

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

Frequently asked(5)

What is CVE-2026-34831?
CVE-2026-34831 is a medium vulnerability published on April 2, 2026. Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than…
When was CVE-2026-34831 disclosed?
CVE-2026-34831 was first published in the National Vulnerability Database on April 2, 2026, with the most recent update on April 16, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-34831 actively exploited?
CVE-2026-34831 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 4.4% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-34831?
CVE-2026-34831 has a CVSS v3 base score of 4.8 (NVD).
How do I remediate CVE-2026-34831?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-34831, 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.

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