CVE-2026-88899

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-09-10. a secondary CVSS source baseline 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this week
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.8Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

knowns versions before 0.31.0 fail to properly validate the x-opencode-directory request header in the /api/opencode proxy endpoint. Remote attackers can supply arbitrary directory paths to execute file operations outside the project root on the host system.

CVSS v3
9.8
EG Score
9.8(high)
EG Risk
59(Track)
EG Risk 59/100SSVC: 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
Severity98% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
38%
KEV
Not listed

Published

September 10, 2026

Last Modified

September 11, 2026

Advisory Details (4)

Auto-updated Sep 18, 2026
🔬 Proof of concept available. Patch available. Sources: github_release, github.
generic

knowns before 0.31.0 External Control of Agent Working Directory via x-opencode-directory Header | Advisories | VulnCheck

https://www.vulncheck.com/advisories/knowns-before-0.31.0-external-control-of-agent-working-directory-via-x-opencode-directory-header
github Patch Available🟡 PoC Available

Sandbox Escape: Unauthenticated Header Injection Grants AI Agent Unrestricted Access to Host Filesystem · Advisory · knowns-dev/knowns · GitHub

https://github.com/knowns-dev/knowns/security/advisories/GHSA-9h2q-r9fh-f98w
github_release Patch Available

v0.31.0

Patch available: knowns-dev/knowns v0.31.0

https://github.com/knowns-dev/knowns/releases/tag/v0.31.0
generic

knowns/internal/server/server.go at v0.30.0 · knowns-dev/knowns · GitHub

https://github.com/knowns-dev/knowns/blob/v0.30.0/internal/server/server.go#L1283-L1296

Vendor Advisories for CVE-2026-88899(1)

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

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 52× in last 7d / 78× 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.

  1. 2026-09-19 18:40 UTCEG score recompute
  2. 2026-09-19 18:40 UTCGHSA enrichment
  3. 2026-09-19 14:24 UTCGHSA enrichment
  4. 2026-09-19 10:09 UTCGHSA enrichment
  5. 2026-09-19 05:54 UTCGHSA enrichment
  6. 2026-09-19 01:40 UTCGHSA enrichment
  7. 2026-09-18 21:24 UTCEG score recompute
  8. 2026-09-18 21:24 UTCGHSA enrichment
  9. 2026-09-18 19:28 UTCEPSS rescore
  10. 2026-09-18 17:09 UTCGHSA enrichment
  11. 2026-09-18 12:54 UTCGHSA enrichment
  12. 2026-09-18 08:39 UTCGHSA enrichment
  13. 2026-09-18 04:24 UTCGHSA enrichment
  14. 2026-09-18 00:09 UTCGHSA enrichment
  15. 2026-09-17 19:54 UTCEG score recompute
  16. 2026-09-17 19:54 UTCGHSA enrichment
  17. 2026-09-17 19:32 UTCEPSS rescore
  18. 2026-09-17 15:36 UTCGHSA enrichment
  19. 2026-09-17 11:20 UTCGHSA enrichment
  20. 2026-09-17 07:04 UTCGHSA enrichment
  21. 2026-09-17 02:48 UTCGHSA enrichment
  22. 2026-09-16 22:26 UTCGHSA enrichment
  23. 2026-09-16 18:09 UTCEG score recompute
  24. 2026-09-16 18:09 UTCGHSA enrichment
  25. 2026-09-16 14:09 UTCEPSS rescore
Show 53 more
  1. 2026-09-16 13:06 UTCGHSA enrichment
  2. 2026-09-16 08:51 UTCEG score recompute
  3. 2026-09-16 08:51 UTCGHSA enrichment
  4. 2026-09-16 05:15 UTCEPSS rescore
  5. 2026-09-16 04:23 UTCGHSA enrichment
  6. 2026-09-16 00:06 UTCGHSA enrichment
  7. 2026-09-15 19:50 UTCGHSA enrichment
  8. 2026-09-15 15:35 UTCGHSA enrichment
  9. 2026-09-15 11:16 UTCGHSA enrichment
  10. 2026-09-15 07:01 UTCEG score recompute
  11. 2026-09-15 07:01 UTCGHSA enrichment
  12. 2026-09-15 03:12 UTCEPSS rescore
  13. 2026-09-15 02:46 UTCGHSA enrichment
  14. 2026-09-14 22:31 UTCGHSA enrichment
  15. 2026-09-14 18:15 UTCGHSA enrichment
  16. 2026-09-14 13:09 UTCGHSA enrichment
  17. 2026-09-14 08:54 UTCGHSA enrichment
  18. 2026-09-14 04:38 UTCGHSA enrichment
  19. 2026-09-14 00:23 UTCGHSA enrichment
  20. 2026-09-13 20:08 UTCEG score recompute
  21. 2026-09-13 20:08 UTCGHSA enrichment
  22. 2026-09-13 16:48 UTCEPSS rescore
  23. 2026-09-13 15:53 UTCGHSA enrichment
  24. 2026-09-13 11:38 UTCGHSA enrichment
  25. 2026-09-13 07:22 UTCGHSA enrichment
  26. 2026-09-13 03:08 UTCGHSA enrichment
  27. 2026-09-12 22:53 UTCGHSA enrichment
  28. 2026-09-12 18:38 UTCEG score recompute
  29. 2026-09-12 18:38 UTCGHSA enrichment
  30. 2026-09-12 15:02 UTCEPSS rescore
  31. 2026-09-12 14:23 UTCGHSA enrichment
  32. 2026-09-12 10:08 UTCGHSA enrichment
  33. 2026-09-12 05:53 UTCGHSA enrichment
  34. 2026-09-12 01:38 UTCGHSA enrichment
  35. 2026-09-11 21:23 UTCEG score recompute
  36. 2026-09-11 21:23 UTCGHSA enrichment
  37. 2026-09-11 20:47 UTCEG score recompute
  38. 2026-09-11 20:47 UTCGHSA enrichment
  39. 2026-09-11 20:08 UTCGHSA enrichment
  40. 2026-09-11 15:33 UTCEG score recompute
  41. 2026-09-11 15:33 UTCGHSA enrichment
  42. 2026-09-11 14:53 UTCEPSS rescore
  43. 2026-09-11 14:53 UTCEPSS rescore
  44. 2026-09-11 11:18 UTCEG score recompute
  45. 2026-09-11 11:17 UTCGHSA enrichment
  46. 2026-09-11 08:48 UTCGHSA enrichment
  47. 2026-09-11 04:33 UTCGHSA enrichment
  48. 2026-09-11 00:18 UTCGHSA enrichment
  49. 2026-09-10 20:03 UTCEG score recompute
  50. 2026-09-10 20:03 UTCGHSA enrichment
  51. 2026-09-10 16:21 UTCEG score recompute
  52. 2026-09-10 15:40 UTCEG score recompute
  53. 2026-09-10 15:39 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-88899?
CVE-2026-88899 is a critical vulnerability published on September 10, 2026. knowns versions before 0.31.0 fail to properly validate the x-opencode-directory request header in the /api/opencode proxy endpoint. Remote attackers can supply arbitrary directory paths to execute file operations outside the project root on the host system.
When was CVE-2026-88899 disclosed?
CVE-2026-88899 was first published in the National Vulnerability Database on September 10, 2026, with the most recent update on September 11, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-88899 actively exploited?
CVE-2026-88899 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 62.5% of all scored CVEs.
What is the CVSS score of CVE-2026-88899?
CVE-2026-88899 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-88899?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-88899, 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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