CVE-2026-55549

MEDIUMPre-NVD 6.56.5
EchelonGraph scoreMEDIUM confidence

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

This medium-severity CVE scores 6.5 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 1.3% (69th percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Elevated
6.5EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 1.3%CVSS: 6.5Exploit: No code on recordExposed services: Not assessed

A fix is available — apply it.

Yamcs is a mission control framework. Prior to 5.9.4, Yamcs reflects an attacker-controlled redirect_uri parameter from GET /auth/authorize into yamcs-core/src/main/resources/auth/templates/authorize.html without adequate HTML escaping by yamcs-core/src/main/java/org/yamcs/http/auth/AuthHandler.java and yamcs-core/src/main/java/org/yamcs/http/HandlerContext.java. A crafted authorization URL can execute JavaScript when opened by a Yamcs user. The script can access browser-held authentication material and transmit it to an attacker, enabling account compromise. This issue is fixed in version 5.9.4.

CVSS v3
6.5
EG Score
6.5MEDIUMmedium confidence
EG Risk
45
EG Risk 45/100

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.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
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 public PoC (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
1.3%
EPSS %ILE
69th
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 public PoC (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

August 28, 2026

Last Modified

September 8, 2026

Advisory Details (3)

Auto-updated Aug 28, 2026
Patch available. Sources: github_release, github, github_commit.
GitHub advisoryMentions a patch (unverified)

Reflected XSS in the URL of the Authorize Endpoint · Advisory · yamcs/yamcs · GitHub

https://github.com/yamcs/yamcs/security/advisories/GHSA-rxpg-wjf8-qv9c
GitHub release Patch Available

Yamcs 5.9.4

Patch available: yamcs/yamcs yamcs-5.9.4

https://github.com/yamcs/yamcs/releases/tag/yamcs-5.9.4
GitHub commit

commit 4d47d5cdcf5d (yamcs/yamcs)

Fix landed in yamcs/yamcs commit 4d47d5cdcf5d — awaiting tagged release

https://github.com/yamcs/yamcs/commit/4d47d5cdcf5d92c2c5bbbc19feada422923332e3

Vendor Advisories for CVE-2026-55549(1)

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

Affected Packages

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFix by version rangeDependents
org.yamcs:yamcs-core0.29.3 ... 5.9.3 (121 versions)
  • every version up to 5.9.4: fixed in 5.9.4
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 14× in last 7d / 52× 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.

  1. 2026-10-13 16:34 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  2. 2026-10-12 16:34 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  3. 2026-10-12 15:55 UTCEG score recompute
  4. 2026-10-11 19:39 UTCEG score recompute
  5. 2026-10-11 16:54 UTCEG score recompute
  6. 2026-10-11 14:17 UTCEG score recompute
  7. 2026-10-11 13:49 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  8. 2026-10-10 20:00 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  9. 2026-10-10 05:58 UTCEG score recompute
  10. 2026-10-09 20:07 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  11. 2026-10-09 06:21 UTCEG score recompute
  12. 2026-10-08 17:12 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  13. 2026-10-08 06:45 UTCEG score recompute
  14. 2026-10-07 23:48 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  15. 2026-10-07 07:04 UTCEG score recompute
  16. 2026-10-06 15:18 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  17. 2026-10-06 07:27 UTCEG score recompute
  18. 2026-10-05 17:43 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  19. 2026-10-04 05:37 UTCEG score recompute
  20. 2026-10-03 14:26 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  21. 2026-10-03 06:02 UTCEG score recompute
  22. 2026-10-02 17:56 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  23. 2026-10-02 06:16 UTCEG score recompute
  24. 2026-10-01 19:50 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  25. 2026-10-01 06:02 UTCEG score recompute
Show 55 more
  1. 2026-09-30 15:03 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  2. 2026-09-30 06:26 UTCEG score recompute
  3. 2026-09-29 15:22 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  4. 2026-09-29 06:50 UTCEG score recompute
  5. 2026-09-28 13:51 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  6. 2026-09-28 07:15 UTCEG score recompute
  7. 2026-09-27 13:48 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  8. 2026-09-27 07:40 UTCEG score recompute
  9. 2026-09-26 15:59 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  10. 2026-09-26 08:04 UTCEG score recompute
  11. 2026-09-24 19:27 UTCEG score recompute
  12. 2026-09-24 14:04 UTCEPSS rescoreEPSS 1.3% · 69th percentile
  13. 2026-09-23 19:52 UTCEG score recompute
  14. 2026-09-23 17:54 UTCEPSS rescoreEPSS 0.9% · 58th percentile
  15. 2026-09-22 19:49 UTCEG score recompute
  16. 2026-09-20 20:39 UTCEG score recompute
  17. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.9% · 58th percentile
  18. 2026-09-19 21:04 UTCEG score recompute
  19. 2026-09-18 21:28 UTCEG score recompute
  20. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  21. 2026-09-17 21:12 UTCEG score recompute
  22. 2026-09-17 19:31 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  23. 2026-09-16 21:36 UTCEG score recompute
  24. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  25. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  26. 2026-09-15 22:01 UTCEG score recompute
  27. 2026-09-15 03:11 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  28. 2026-09-13 22:45 UTCEG score recompute
  29. 2026-09-13 16:47 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  30. 2026-09-12 23:10 UTCEG score recompute
  31. 2026-09-11 23:34 UTCEG score recompute
  32. 2026-09-11 14:53 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  33. 2026-09-10 23:58 UTCEG score recompute
  34. 2026-09-10 09:35 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  35. 2026-09-09 23:52 UTCEG score recompute
  36. 2026-09-08 22:01 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  37. 2026-09-07 23:35 UTCEG score recompute
  38. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  39. 2026-09-06 23:59 UTCEG score recompute
  40. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  41. 2026-09-06 00:24 UTCEG score recompute
  42. 2026-09-05 00:49 UTCEG score recompute
  43. 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  44. 2026-09-03 01:36 UTCEG score recompute
  45. 2026-09-02 14:12 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  46. 2026-09-02 01:58 UTCEG score recompute
  47. 2026-09-01 13:54 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  48. 2026-09-01 04:40 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  49. 2026-09-01 02:23 UTCEG score recompute
  50. 2026-09-01 02:10 UTCEG score recompute
  51. 2026-08-30 19:35 UTCEG score recompute
  52. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.4% · 29th percentile
  53. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.4% · 28th percentile
  54. 2026-08-28 20:25 UTCEG score recompute
  55. 2026-08-28 18:10 UTCEG score recomputeFirst assessed: 6.5 MEDIUM

Public detection templates

(1 reference)

A public Nuclei detection template is referenced for this CVE. A detection template checks whether a system is affected; it is not necessarily exploit code.

  • Nucleihttp/cves/2026/CVE-2026-55549.yaml
    Published Sep 18, 2026

    Yamcs <=5.8.6 - Cross-Site Scripting

    Open source ↗

Related CVEs(same product + same CWE)

Frequently asked(5)

What is CVE-2026-55549?
CVE-2026-55549 is a medium-severity vulnerability; its CVE record was published on August 28, 2026. Yamcs is a mission control framework. Prior to 5.9.4, Yamcs reflects an attacker-controlled redirect_uri parameter from GET /auth/authorize into yamcs-core/src/main/resources/auth/templates/authorize.html without adequate HTML escaping by…
When was the CVE record for CVE-2026-55549 published?
The CVE record for CVE-2026-55549 was published on August 28, 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 8, 2026; the record at its source may have been updated since.
Is CVE-2026-55549 actively exploited?
CVE-2026-55549 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 1.3% probability of exploitation in the next 30 days (69th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-55549?
CVE-2026-55549 has a CVSS base score of 6.5 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-55549?
A fix for CVE-2026-55549 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-55549 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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