CVE-2026-5163

MEDIUMNVD 6.56.5
EchelonGraph scoreMEDIUM confidence

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

Score 6.5 from GitHub Security Advisory published 2026-05-18. NVD baseline CVSS 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, NVD CVSS v3
6.5EG
EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 6.5Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

Fixed versions, as the CVE record's CNA (Mattermost, Inc.) states them: "Update Mattermost to versions 11.6.0, 11.5.2 or higher."

Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint.. Mattermost Advisory ID: MMSA-2026-00645

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
29
EG Risk 29/100

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)
Severity65% × 45%
The EG Score, 6.5 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 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
25th
KEV
Not listed

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.

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

May 18, 2026

Last Modified

May 18, 2026

Advisory Details (1)

Auto-updated May 18, 2026
Patch available.
Web page

Security Updates

https://mattermost.com/security-updates

Vendor Advisories for CVE-2026-5163(1)

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

Affected Packages

(4 across 1 ecosystem)
Go(4)
PackageVulnerable rangeFix by version rangeDependents
github.com/mattermost/mattermost-server—
  • every version up to 5.3.2-0.20260401090745-f4d1abe7e8f5: fixed in 5.3.2-0.20260401090745-f4d1abe7e8f5
  • 11.5.0+incompatible up to 11.5.2+incompatible: fixed in 11.5.2+incompatible
—
github.com/mattermost/mattermost-server/v5—
  • every version on: no fix on record
—
github.com/mattermost/mattermost-server/v6—
  • every version on: no fix on record
—
github.com/mattermost/mattermost/server/v8—
  • 11.5.0 up to 11.5.2: fixed in 11.5.2
  • every version up to 8.0.0-20260401090745-f4d1abe7e8f5: fixed in 8.0.0-20260401090745-f4d1abe7e8f5
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 11× in last 7d / 30× 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 94 of 176 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. 6 repeat rows among the latest 100 are merged into the row they repeat. The 82 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  2. 2026-10-12 15:58 UTCEG score recompute
  3. 2026-10-11 19:41 UTCEG score recompute
  4. 2026-10-11 16:56 UTCEG score recompute
  5. 2026-10-11 14:20 UTCEG score recompute
  6. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  7. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  8. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  9. 2026-10-08 17:13 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  10. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  11. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  12. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  13. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  14. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  15. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  16. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  17. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  18. 2026-09-30 03:40 UTCOSV refresh
  19. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  20. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  21. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  22. 2026-09-24 14:04 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  23. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  24. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  25. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.2% · 10th percentile
Show 69 more
  1. 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  2. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  3. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  4. 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  5. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  6. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  7. 2026-09-11 06:23 UTCOSV refresh
  8. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  9. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  10. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  11. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  12. 2026-09-04 05:07 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  13. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  14. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  15. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  16. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  17. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  18. 2026-08-28 21:42 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  19. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  20. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  21. 2026-08-25 13:49 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  22. 2026-08-23 17:17 UTCEG score recompute
  23. 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  24. 2026-08-22 00:20 UTCEG score recompute
  25. 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  26. 2026-08-20 22:55 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  27. 2026-08-20 19:11 UTCEG score recompute
  28. 2026-08-19 17:04 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  29. 2026-08-18 13:48 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  30. 2026-08-17 13:47 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  31. 2026-08-17 10:08 UTCEG score recompute
  32. 2026-08-16 14:56 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  33. 2026-08-16 03:41 UTCEG score recompute
  34. 2026-08-15 01:30 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  35. 2026-08-14 02:13 UTCEG score recompute
  36. 2026-08-13 22:00 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  37. 2026-08-12 20:34 UTCEG score recompute
  38. 2026-08-12 13:51 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  39. 2026-08-11 22:39 UTCEG score recompute
  40. 2026-08-11 00:44 UTCEG score recompute
  41. 2026-08-11 00:00 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  42. 2026-08-09 23:36 UTCEG score recompute
  43. 2026-08-09 13:46 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  44. 2026-08-09 01:41 UTCEG score recompute
  45. 2026-08-08 16:37 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  46. 2026-08-07 17:17 UTCEG score recompute
  47. 2026-08-06 19:22 UTCEG score recompute
  48. 2026-08-06 13:47 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  49. 2026-08-05 21:26 UTCEG score recompute
  50. 2026-08-05 19:17 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  51. 2026-08-04 15:10 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  52. 2026-08-04 10:39 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  53. 2026-08-03 17:08 UTCEG score recompute
  54. 2026-08-03 10:36 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  55. 2026-08-02 16:32 UTCEG score recompute
  56. 2026-08-02 02:27 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  57. 2026-08-01 18:36 UTCEG score recompute
  58. 2026-08-01 04:16 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  59. 2026-07-30 16:28 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  60. 2026-07-30 01:30 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  61. 2026-07-28 15:37 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  62. 2026-07-27 14:14 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  63. 2026-07-26 14:54 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  64. 2026-07-25 14:18 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  65. 2026-07-23 14:18 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  66. 2026-07-23 03:19 UTCEG score recompute
  67. 2026-07-22 14:08 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  68. 2026-07-21 15:25 UTCEPSS rescoreEPSS 0.2% · 10th percentile
  69. 2026-07-20 17:08 UTCEPSS rescoreEPSS 0.2% · 10th percentile

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-5163?
CVE-2026-5163 is a medium-severity vulnerability; its CVE record was published on May 18, 2026. Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite…
When was the CVE record for CVE-2026-5163 published?
The CVE record for CVE-2026-5163 was published on May 18, 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 May 18, 2026; the record at its source may have been updated since.
Is CVE-2026-5163 actively exploited?
CVE-2026-5163 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (25th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-5163?
CVE-2026-5163 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-5163?
A fix for CVE-2026-5163 is available: update to the fixed version the vendor names in its advisory. Fixed versions, as the CVE record's CNA (Mattermost, Inc.) states them: "Update Mattermost to versions 11.6.0, 11.5.2 or higher." The vendor advisories EchelonGraph has for CVE-2026-5163 are linked in the Vendor Advisories panel on this page.

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