CVE-2026-39821

CRITICALPre-NVD 9.610.0▲
EchelonGraph scoreMEDIUM confidence

Score 10.0 from GitHub Security Advisory (severity: CRITICAL) published 2026-05-26. CISA-ADP (Vulnrichment) CVSS v3.1 baseline 9.6; sources differ by 0.4.

Triggered by: GitHub Security Advisory CVSS
Sources: cisa-adp, epss, ghsa
Trending — Patch released this week
10.0EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 1%CVSS: 9.6Exploit: None knownExposed: 0

A fix is available — apply it.

The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com") incorrectly returns the name "example.com" rather than an error. This behavior can lead to privilege escalation in programs using the idna package. For example, a program which performs privilege checks on the ASCII hostname may reject "example.com" but permit "xn--example-.com". If that program subsequently converts the ASCII hostname to Unicode, it will inadvertently permits access to the Unicode name "example.com".

CVSS v3
9.6
EG Score
10.0(medium)
EG Risk
45(Track)
EG Risk 45/100SSVC: 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
Severity100% × 45%
Exploitation1% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
1%
EPSS %ILE
48%
KEV
Not listed

Published

May 22, 2026

Last Modified

July 24, 2026

Advisory Details (4)

Auto-updated May 23, 2026
No patch confirmed yet.
generic

GO-2026-5026 - Go Packages

https://pkg.go.dev/vuln/GO-2026-5026
generic
https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8
generic

x/net/idna: ToUnicode accepts Punycode labels encoding pure ASCII labels · Issue #78760 · golang/go · GitHub

https://go.dev/issue/78760
generic
https://go.dev/cl/767220

Vendor Advisories for CVE-2026-39821(20)

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

Patch Availability(25)

Vendor / EcosystemFixed in / PatchReleasedSource
redhatmulticluster-globalhub/multicluster-globalhub-agent-rhel9:17841520462026-07-23redhat
redhatrhosdt/tempo-rhel9-operator:17847757822026-07-23redhat
redhatoadp/oadp-velero-rhel9:17840588222026-07-22redhat
redhatquay/quay-rhel8:17843519662026-07-21redhat
redhatquay/quay-rhel8:17843539042026-07-21redhat
redhatmulticluster-globalhub/multicluster-globalhub-agent-rhel9:17841274912026-07-21redhat
redhatrhoai/odh-training-operator-rhel9:17839463862026-07-21redhat
redhatmta/mta-cli-rhel9:17842113782026-07-21redhat
redhatyggdrasil-worker-forwarder-0:0.0.4-1.el9sat2026-07-20redhat
redhatreceptor-0:1.6.6-1.el9ap2026-07-20redhat
redhatweb-terminal/web-terminal-exec-rhel9:17842962032026-07-20redhat
redhatweb-terminal/web-terminal-exec-rhel9:17842961142026-07-20redhat
redhatweb-terminal/web-terminal-exec-rhel9:17842476102026-07-20redhat
redhatrhmtc/openshift-migration-controller-rhel8:17839533722026-07-20redhat
redhatweb-terminal/web-terminal-exec-rhel9:17842957672026-07-20redhat
redhatweb-terminal/web-terminal-exec-rhel9:17842960332026-07-20redhat
redhatquay/quay-rhel8:17837518652026-07-20redhat
redhatweb-terminal/web-terminal-exec-rhel9:17842961272026-07-20redhat
redhatansible-automation-platform-27/receptor-rhel9:17839179632026-07-20redhat
redhatansible-automation-platform-26/receptor-rhel9:17839624642026-07-20redhat
redhatrhc-1:0.2.5-9.el8_102026-07-20redhat
redhatquay/quay-rhel8:17837504472026-07-16redhat
redhatmulticluster-globalhub/multicluster-globalhub-agent-rhel9:17840614722026-07-16redhat
redhatmulticluster-engine/discovery-rhel9:17839859992026-07-16redhat
redhatrhem/flightctl-ui-rhel10:17841945742026-07-16redhat

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)
Go(1)
PackageVulnerable rangeFixed inDependents
golang.org/x/net—0.55.0—

Weakness Classification(1)

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

All Vendor Advisories

(25)

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 15× in last 7d / 56× 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 327 total refreshes for this CVE.

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

Frequently asked(5)

What is CVE-2026-39821?
CVE-2026-39821 is a critical vulnerability published on May 22, 2026. The ToASCII and ToUnicode functions incorrectly accept Punycode-encoded labels that decode to an ASCII-only label. For example, ToUnicode("xn--example-.com") incorrectly returns the name "example.com" rather than an error. This behavior can lead to privilege escalation in programs using the idna…
When was CVE-2026-39821 disclosed?
CVE-2026-39821 was first published in the National Vulnerability Database on May 22, 2026, with the most recent update on July 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-39821 actively exploited?
CVE-2026-39821 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1% probability of exploitation in the next 30 days, which ranks it in the top 52.4% of all scored CVEs.
What is the CVSS score of CVE-2026-39821?
CVE-2026-39821 has a CVSS v3.1 base score of 9.6 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 10.0.
How do I remediate CVE-2026-39821?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-39821, 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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