CVE-2026-39821

CRITICALPre-NVD 9.610.0
EchelonGraph scoreMEDIUM confidence

“▲” beside the score: it is higher than the CVSS score beside it.

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 (Vulnrichment) CVSS v3.1, EPSS, GitHub Security Advisory
Trending — Patch released this week

Also known asEUVD-2026-31449 (ENISA EUVD) · GHSA-w2q5-6q6x-x959 (GitHub Security Advisories)Source: ENISA EUVD

10.0EG
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: 1.8%CVSS: 9.6Exploit: None knownExposed services: Not assessed

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
10.0CRITICALmedium confidence
EG Risk
46
EG Risk 46/100

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)
Severity100% × 45%
Impact severity (EG Severity): CVSS 10.0 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation1.8% × 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 low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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
1.8%
EPSS %ILE
78th
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 (10.0): severity, escalated by confirmed exploitation. This CVE's 10.0 is its impact severity (EG Severity), not escalated.

EG Severity
10.0 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
1.8% 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 low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 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 low or medium mission impact; Track* at high (mission-essential systems).

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

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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)14 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 total (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

May 22, 2026

Last Modified

September 17, 2026

Advisory Details (11)

Auto-updated Oct 7, 2026
Patch available. Sources: redhat.
Red HatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:30650
Red HatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:26547
Red HatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:26546
Red HatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:23264
Red HatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:23262
Web page

GO-2026-5026 - Go Packages

https://pkg.go.dev/vuln/GO-2026-5026
Web page
https://groups.google.com/g/golang-announce/c/iI-mYSI0lu8
Web page
https://groups.google.com/g/golang-announce/c/94pEornpRlI
Web page

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

https://go.dev/issue/78760
Web page
https://go.dev/cl/767220
Red HatMentions a patch (unverified)
https://access.redhat.com/errata/RHSA-2026:30651

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(30)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatrhc-1:0.2.0-6.el8_4.22026-10-29redhat
redhatrhoai/odh-ml-pipelines-scheduledworkflow-v2-rhel9:17927259992026-10-29redhat
redhatrhc-1:0.2.2-1.el8_8.32026-10-27redhat
redhatopenshift4/ose-kube-rbac-proxy-rhel9:17927747852026-10-27redhat
redhatgo-toolset:rhel8-8040020261027035356.522a0ee42026-10-27redhat
redhatrhc-1:0.2.1-14.el8_6.12026-10-27redhat
redhatopenshift-clients-0:4.14.0-202610221646.p2.g92da620.assembly.stream.el82026-10-27redhat
redhatopenshift4/ose-cli:17928887572026-10-27redhat
redhatetcd-0:3.4.26-9.10.el9ost2026-10-26redhat
redhatopenshift4/ose-kube-rbac-proxy-rhel9:17928492452026-10-26redhat
redhatopenshift4/ose-kube-rbac-proxy-rhel9:17928533782026-10-26redhat
redhatopenshift-builds/openshift-builds-rhel10-operator:17927493582026-10-24redhat
redhatopenshift-builds/openshift-builds-rhel10-operator:17928596292026-10-24redhat
redhatgrafana-pcp-0:3.2.0-4.el8_6.22026-10-22redhat
redhatgrafana-0:7.5.15-12.el8_82026-10-22redhat
redhatgrafana-pcp-0:3.2.0-6.el8_8.22026-10-22redhat
redhatgrafana-0:7.5.11-12.el8_62026-10-22redhat
redhatgo-toolset:rhel8-8080020261020152326.6b4b45d82026-10-21redhat
redhatrhoai/odh-feast-operator-rhel9:17918615032026-10-21redhat
redhatgo-toolset:rhel8-8060020261020153812.97d7f71f2026-10-21redhat
redhatose-gcp-gcr-image-credential-provider-0:4.22.0-202610051811.p2.gdf2fcb8.assembly.stream.el82026-10-21redhat
redhatrhoai/odh-trustyai-service-operator-rhel9:17912923522026-10-19redhat
redhatopenshift4/frr-rhel9:17908542632026-10-15redhat
redhatose-aws-ecr-image-credential-provider-0:4.16.0-202610062120.p2.gac983ec.assembly.stream.el82026-10-15redhat
redhatopenshift4/frr-rhel9:17908265452026-10-15redhat
redhatopenshift4/frr-rhel9:17906284602026-10-08redhat
redhatopenshift4/frr-rhel9:17906099252026-10-07redhat
redhatcompliance/openshift-security-profiles-rhel8-operator:17906230302026-10-06redhat
redhatopenshift4/frr-rhel9:17907027432026-10-06redhat
redhatgrafana-0:9.0.9-13.el9_22026-10-06redhat

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

(6 across 5 ecosystems)
Go(2)
PackageVulnerable rangeFix by version rangeDependents
golang.org/x/net—
  • every version up to 0.55.0: fixed in 0.55.0
—
stdlib—
  • every version up to 1.25.13: fixed in 1.25.13
  • 1.26.0-0 up to 1.26.6: fixed in 1.26.6
  • 1.27.0-0 up to 1.27.0-rc.3: fixed in 1.27.0-rc.3
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
golang-golang-x-net1:0.0+git20210119.5f4716e+dfsg-4 ... 1:0.7.0+dfsg-1 (40 versions)
  • every version on: no fix on record
—
Debian:12(1)
PackageVulnerable rangeFix by version rangeDependents
golang-golang-x-net1:0.10.0-1 ... 1:0.7.0+dfsg-1 (27 versions)
  • every version on: no fix on record
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
golang-golang-x-net1:0.27.0-2 ... 1:0.58.0-1 (10 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
golang-golang-x-net1:0.27.0-2 ... 1:0.53.0-2~bpo13+1 (6 versions)
  • every version up to 1:0.55.0-1: fixed in 1:0.55.0-1
—

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 30× in last 7d / 103× 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 799 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 699 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-11-02 00:45 UTCEG score recompute
  2. 2026-11-02 00:45 UTCVendor advisory
  3. 2026-11-02 00:45 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  4. 2026-11-01 16:34 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  5. 2026-11-01 02:57 UTCEG score recompute
  6. 2026-11-01 02:57 UTCVendor advisory
  7. 2026-11-01 02:57 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  8. 2026-10-31 16:32 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  9. 2026-10-31 05:09 UTCEG score recompute
  10. 2026-10-31 05:09 UTCVendor advisory
  11. 2026-10-31 05:09 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  12. 2026-10-30 16:34 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  13. 2026-10-30 07:21 UTCEG score recompute
  14. 2026-10-30 07:21 UTCVendor advisory
  15. 2026-10-30 07:21 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  16. 2026-10-29 16:33 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  17. 2026-10-29 09:33 UTCEG score recompute
  18. 2026-10-29 09:33 UTCVendor advisory
  19. 2026-10-29 09:33 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  20. 2026-10-28 16:32 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  21. 2026-10-28 11:46 UTCEG score recompute
  22. 2026-10-28 11:46 UTCVendor advisory
  23. 2026-10-28 11:46 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  24. 2026-10-27 16:31 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  25. 2026-10-27 13:47 UTCEG score recompute
Show 75 more
  1. 2026-10-27 13:47 UTCVendor advisory
  2. 2026-10-27 13:47 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  3. 2026-10-26 16:31 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  4. 2026-10-26 15:26 UTCVendor advisory
  5. 2026-10-26 15:26 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  6. 2026-10-25 16:58 UTCEG score recompute
  7. 2026-10-25 16:58 UTCVendor advisory
  8. 2026-10-25 16:58 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  9. 2026-10-25 16:32 UTCEPSS rescoreEPSS 1.8% · 78th percentile
  10. 2026-10-25 14:31 UTCEG score recompute
  11. 2026-10-24 19:10 UTCEG score recompute
  12. 2026-10-24 19:10 UTCVendor advisory
  13. 2026-10-24 19:10 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  14. 2026-10-24 16:32 UTCEPSS rescoreEPSS 0.7% · 52nd percentile
  15. 2026-10-23 21:20 UTCEG score recompute
  16. 2026-10-23 21:20 UTCVendor advisory
  17. 2026-10-23 21:19 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  18. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.7% · 52nd percentile
  19. 2026-10-22 23:29 UTCEG score recompute
  20. 2026-10-22 23:29 UTCVendor advisory
  21. 2026-10-22 23:28 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  22. 2026-10-22 16:34 UTCEPSS rescoreEPSS 0.7% · 52nd percentile
  23. 2026-10-22 01:39 UTCEG score recompute
  24. 2026-10-22 01:39 UTCVendor advisory
  25. 2026-10-22 01:39 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  26. 2026-10-21 16:33 UTCEPSS rescoreEPSS 0.7% · 52nd percentile
  27. 2026-10-21 03:51 UTCEG score recompute
  28. 2026-10-21 03:51 UTCVendor advisory
  29. 2026-10-21 03:51 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  30. 2026-10-20 16:33 UTCEPSS rescoreEPSS 0.7% · 52nd percentile
  31. 2026-10-20 05:48 UTCEG score recompute
  32. 2026-10-20 05:48 UTCVendor advisory
  33. 2026-10-20 05:48 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  34. 2026-10-19 16:32 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  35. 2026-10-19 07:25 UTCEG score recompute
  36. 2026-10-19 07:25 UTCVendor advisory
  37. 2026-10-19 07:25 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  38. 2026-10-18 16:32 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  39. 2026-10-18 09:25 UTCVendor advisory
  40. 2026-10-18 09:25 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  41. 2026-10-18 03:43 UTCEG score recompute
  42. 2026-10-17 16:34 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  43. 2026-10-17 10:59 UTCEG score recompute
  44. 2026-10-17 10:59 UTCVendor advisory
  45. 2026-10-17 10:58 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  46. 2026-10-16 16:41 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  47. 2026-10-16 12:32 UTCEG score recompute
  48. 2026-10-16 12:32 UTCVendor advisory
  49. 2026-10-16 12:32 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  50. 2026-10-15 16:32 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  51. 2026-10-15 14:25 UTCEG score recompute
  52. 2026-10-15 14:25 UTCVendor advisory
  53. 2026-10-15 14:25 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  54. 2026-10-14 16:32 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  55. 2026-10-14 09:06 UTCEG score recompute
  56. 2026-10-14 09:06 UTCVendor advisory
  57. 2026-10-14 09:06 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  58. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  59. 2026-10-13 05:59 UTCEG score recompute
  60. 2026-10-13 05:59 UTCVendor advisory
  61. 2026-10-13 05:59 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  62. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  63. 2026-10-12 16:10 UTCEG score recompute
  64. 2026-10-12 08:09 UTCVendor advisory
  65. 2026-10-12 08:08 UTCGHSA enrichmentGHSA-w2q5-6q6x-x959 · GitHub severity CRITICAL · GitHub CVSS 10.0
  66. 2026-10-11 19:52 UTCEG score recompute
  67. 2026-10-11 17:05 UTCEG score recompute
  68. 2026-10-11 14:32 UTCEG score recompute
  69. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  70. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  71. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  72. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  73. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.7% · 51st percentile
  74. 2026-10-07 06:35 UTCOSV refresh
  75. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.7% · 51st percentile

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

Frequently asked(5)

What is CVE-2026-39821?
CVE-2026-39821 is a critical-severity vulnerability; its CVE record was 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 the CVE record for CVE-2026-39821 published?
The CVE record for CVE-2026-39821 was published on May 22, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 17, 2026; the record at its source may have been updated since.
Is CVE-2026-39821 actively exploited?
CVE-2026-39821 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.8% probability of exploitation in the next 30 days (78th percentile of EPSS-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 CISA-ADP (Vulnrichment) CVSS v3.1 + FIRST EPSS + GHSA into a combined EG score of 10.0 (CRITICAL).
How do I remediate CVE-2026-39821?
A fix for CVE-2026-39821 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-39821 are linked in the Vendor Advisories panel on this page.

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