CVE-2026-55999

HIGHNVD 7.88.5
EchelonGraph scoreMEDIUM confidence

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

Score 8.5 from GitHub Security Advisory (severity: HIGH) published 2026-07-08. NVD baseline CVSS 7.8; sources differ by 0.7.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
8.5EG
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: 7.8Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Local attackers with a X connection able to provide PCX fonts to the X server xorg-server before 21.2.24 and xwayland before 24.1.13 could cause a heap buffer overflow via SetFont due to missing glyph boundary checks.

CVSS v3
7.8
EG Score
8.5HIGHmedium confidence
EG Risk
38
EG Risk 38/100

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 (value × EchelonGraph’s weight)
Severity85% × 45%
The EG Score, 8.5 of 10.
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 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
0.3%
EPSS %ILE
24th
KEV
Not listed

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.

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

July 8, 2026

Last Modified

July 9, 2026

Advisory Details (2)

Auto-updated Jul 8, 2026
Patch available.
Web page

oss-security - FW: X.Org Security Advisory: multiple security issues X.Org X server and Xwayland

https://www.openwall.com/lists/oss-security/2026/07/08/2
Web page

glamor: reject fonts with per-glyph metrics exceeding maxbounds (fbf7bac2) · Commits · xorg / xserver · GitLab

https://gitlab.freedesktop.org/xorg/xserver/-/commit/fbf7bac22e2c6bd627fb042742a23318263edae1

Vendor Advisories for CVE-2026-55999(20)

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

Patch Availability(18)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
redhatxorg-x11-server-Xwayland-0:21.1.3-2.el8_6.82026-08-11redhat
redhatxorg-x11-server-Xwayland-0:21.1.3-13.el8_8.22026-08-10redhat
redhatxorg-x11-server-Xwayland-0:21.1.3-10.el9_2.22026-08-10redhat
redhatxorg-x11-server-Xwayland-0:22.1.9-8.el9_4.32026-08-10redhat
redhatxorg-x11-server-Xwayland-0:23.2.7-6.el9_6.32026-08-05redhat
redhatxorg-x11-server-0:1.20.4-36.el7_92026-08-04redhat
redhatxorg-x11-server-0:1.20.11-19.el8_8.12026-08-04redhat
redhatxorg-x11-server-Xwayland-0:24.1.5-6.el10_0.22026-08-04redhat
redhatxorg-x11-server-0:1.20.11-34.el9_6.12026-08-03redhat
redhatxorg-x11-server-0:1.20.11-29.el9_4.12026-08-03redhat
redhatxorg-x11-server-0:1.20.10-5.el8_4.12026-08-03redhat
redhatxorg-x11-server-0:1.20.11-8.el8_6.12026-08-03redhat
redhatxorg-x11-server-0:1.20.11-21.el9_2.12026-08-03redhat
redhatxorg-x11-server-Xwayland-0:21.1.3-20.el8_10.32026-07-13redhat
redhatxorg-x11-server-Xwayland-0:24.1.9-4.el9_8.32026-07-13redhat
redhatxorg-x11-server-Xwayland-0:24.1.9-4.el10_2.32026-07-13redhat
redhatxorg-x11-server-0:1.20.11-28.el8_10.32026-07-13redhat
redhatxorg-x11-server-0:1.20.11-34.el9_8.32026-07-13redhat

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

(7 across 4 ecosystems)
Debian:12(2)
PackageVulnerable rangeFix by version rangeDependents
xorg-server2:21.1.10-1 ... 2:21.1.9-1+hurd.1 (42 versions)
  • every version on: no fix on record
—
xwayland2:22.1.9-1 ... 2:24.1.9-1 (24 versions)
  • every version on: no fix on record
—
Debian:13(2)
PackageVulnerable rangeFix by version rangeDependents
xorg-server2:21.1.16-1.3, 2:21.1.16-1.3+deb13u1, 2:21.1.16-1.3+deb13u2, 2:21.1.16-1.3+deb13u3
  • every version up to 2:21.1.16-1.3+deb13u4: fixed in 2:21.1.16-1.3+deb13u4
—
xwayland2:24.1.10-1 ... 2:24.1.9-1 (7 versions)
  • every version on: no fix on record
—
Debian:14(2)
PackageVulnerable rangeFix by version rangeDependents
xorg-server2:21.1.16-1.3 ... 2:21.1.23-1 (7 versions)
  • every version up to 2:21.1.24-1: fixed in 2:21.1.24-1
—
xwayland2:24.1.10-1 ... 2:24.1.9-1 (6 versions)
  • every version up to 2:24.1.13-1: fixed in 2:24.1.13-1
—
Debian:11(1)
PackageVulnerable rangeFix by version rangeDependents
xorg-server2:1.20.11-1 ... 2:21.1.9-1+hurd.1 (61 versions)
  • every version on: no fix on record
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 11× in last 7d / 45× 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 335 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 235 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  2. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  3. 2026-10-12 15:55 UTCEG score recompute
  4. 2026-10-11 19:38 UTCEG score recompute
  5. 2026-10-11 16:53 UTCEG score recompute
  6. 2026-10-11 14:16 UTCEG score recompute
  7. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  8. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  9. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  10. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  11. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  12. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  13. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  14. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  15. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  16. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  17. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  18. 2026-10-01 16:21 UTCEG score recompute
  19. 2026-10-01 16:21 UTCVendor advisory
  20. 2026-10-01 16:21 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  21. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  22. 2026-09-29 15:22 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  23. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  24. 2026-09-28 13:26 UTCEG score recompute
  25. 2026-09-28 13:26 UTCVendor advisory
Show 75 more
  1. 2026-09-28 13:26 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  2. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  3. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  4. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  5. 2026-09-24 11:54 UTCEG score recompute
  6. 2026-09-24 11:54 UTCVendor advisory
  7. 2026-09-24 11:54 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  8. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  9. 2026-09-23 06:13 UTCEG score recompute
  10. 2026-09-23 06:13 UTCVendor advisory
  11. 2026-09-23 06:13 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  12. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  13. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  14. 2026-09-18 05:46 UTCEG score recompute
  15. 2026-09-18 05:46 UTCVendor advisory
  16. 2026-09-18 05:46 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  17. 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  18. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  19. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  20. 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  21. 2026-09-14 11:17 UTCVendor advisory
  22. 2026-09-14 11:17 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  23. 2026-09-13 23:51 UTCEG score recompute
  24. 2026-09-13 23:51 UTCVendor advisory
  25. 2026-09-13 23:51 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  26. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.3% · 19th percentile
  27. 2026-09-13 08:27 UTCEG score recompute
  28. 2026-09-13 08:27 UTCVendor advisory
  29. 2026-09-13 08:27 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  30. 2026-09-12 14:36 UTCVendor advisory
  31. 2026-09-12 14:36 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  32. 2026-09-12 03:39 UTCEG score recompute
  33. 2026-09-12 03:39 UTCVendor advisory
  34. 2026-09-12 03:39 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  35. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  36. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  37. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  38. 2026-09-06 14:07 UTCEG score recompute
  39. 2026-09-06 14:07 UTCVendor advisory
  40. 2026-09-06 14:06 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  41. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  42. 2026-09-05 22:50 UTCEG score recompute
  43. 2026-09-05 22:50 UTCVendor advisory
  44. 2026-09-05 22:50 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  45. 2026-09-04 05:07 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  46. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  47. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  48. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  49. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  50. 2026-08-30 18:36 UTCVendor advisory
  51. 2026-08-30 18:36 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  52. 2026-08-30 07:39 UTCEG score recompute
  53. 2026-08-30 07:39 UTCVendor advisory
  54. 2026-08-30 07:39 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  55. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  56. 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  57. 2026-08-27 21:52 UTCEG score recompute
  58. 2026-08-27 21:52 UTCVendor advisory
  59. 2026-08-27 21:52 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  60. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  61. 2026-08-27 01:45 UTCEG score recompute
  62. 2026-08-27 01:45 UTCVendor advisory
  63. 2026-08-27 01:45 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  64. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  65. 2026-08-26 08:30 UTCEG score recompute
  66. 2026-08-26 08:30 UTCVendor advisory
  67. 2026-08-26 08:30 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  68. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.3% · 18th percentile
  69. 2026-08-25 07:41 UTCVendor advisory
  70. 2026-08-25 07:41 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  71. 2026-08-24 20:42 UTCEG score recompute
  72. 2026-08-24 20:42 UTCVendor advisory
  73. 2026-08-24 20:42 UTCGHSA enrichmentGHSA-h655-847g-q4f7 · GitHub severity HIGH · GitHub CVSS 8.5
  74. 2026-08-24 09:45 UTCEG score recompute
  75. 2026-08-24 09:45 UTCVendor advisory

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

Same vendor

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redhat:RHSA-2026:38489

Frequently asked(5)

What is CVE-2026-55999?
CVE-2026-55999 is a high-severity vulnerability; its CVE record was published on July 8, 2026. Local attackers with a X connection able to provide PCX fonts to the X server xorg-server before 21.2.24 and xwayland before 24.1.13 could cause a heap buffer overflow via SetFont due to missing glyph boundary checks.
When was CVE-2026-55999 made public?
CVE-2026-55999 was made public on July 8, 2026: that is the date its CVE record's CNA, SUSE, gives for when the vulnerability was made public. The CVE record itself was published on July 8, 2026. EchelonGraph's copy of the record carries a last-modified date of July 9, 2026; the record at its source may have been updated since.
Is CVE-2026-55999 actively exploited?
CVE-2026-55999 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (24th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-55999?
CVE-2026-55999 has a CVSS v3 base score of 7.8 (NVD). EchelonGraph synthesises NVD + CISA KEV + FIRST EPSS + GHSA into a combined EG score of 8.5 (HIGH).
How do I remediate CVE-2026-55999?
A fix for CVE-2026-55999 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-55999 are linked in the Vendor Advisories panel on this page.

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