CVE-2026-53591

HIGHPre-NVD 8.68.6—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.6 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 88% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Elevated
8.6EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.6Exploit: Elevated riskExposed: 0

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

FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to version 1.8.223, an unauthenticated attacker can inject messages into any existing support conversation by sending a single email to the helpdesk's public address with a crafted In-Reply-To header. No credentials, tokens, or prior access are required. The injected message is rendered in the agent UI as a legitimate customer reply, the conversation is automatically reopened, and the last_reply_from field is set to the attacker's identity. Version 1.8.223 contains a fix.

CVSS v3
8.6
EG Score
8.6(medium)
EG Risk
70(Attend)
EG Risk 70/100SSVC: Attend

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
Severity86% × 45%
Exploitation40% × 40%
Automatability100% × 15%
Action: Remediate soon — notable exploitation risk.
EPSS PROB
0%
EPSS %ILE
12%
KEV
Not listed

Published

July 20, 2026

Last Modified

July 21, 2026

Advisory Details (1)

Auto-updated Jul 20, 2026
🔬 Proof of concept available. Patch available. Sources: github.
github Patch Available🟡 PoC Available

Unauthenticated Conversation Thread Injection via HMAC Length Bypass in FetchEmails · Advisory · freescout-help-desk/freescout · GitHub

https://github.com/freescout-help-desk/freescout/security/advisories/GHSA-8vm3-wwq4-ggfx

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 11× in last 7d / 20× 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. 2026-07-31 00:17 UTCEG score recompute
  2. 2026-07-30 16:28 UTCEPSS rescore
  3. 2026-07-30 12:12 UTCEG score recompute
  4. 2026-07-30 01:30 UTCEPSS rescore
  5. 2026-07-28 23:53 UTCEG score recompute
  6. 2026-07-28 15:37 UTCEPSS rescore
  7. 2026-07-27 23:35 UTCEG score recompute
  8. 2026-07-26 22:51 UTCEG score recompute
  9. 2026-07-26 14:54 UTCEPSS rescore
  10. 2026-07-26 10:46 UTCEG score recompute
  11. 2026-07-25 14:18 UTCEPSS rescore
  12. 2026-07-24 14:18 UTCEPSS rescore
  13. 2026-07-23 14:18 UTCEPSS rescore
  14. 2026-07-23 03:19 UTCEG score recompute
  15. 2026-07-22 23:29 UTCEG score recompute
  16. 2026-07-22 14:08 UTCEPSS rescore
  17. 2026-07-21 15:25 UTCEPSS rescore
  18. 2026-07-20 20:42 UTCEG score recompute
  19. 2026-07-20 19:57 UTCEG score recompute
  20. 2026-07-20 19:57 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-53591?
CVE-2026-53591 is a high vulnerability published on July 20, 2026. FreeScout is a free help desk and shared inbox built with PHP's Laravel framework. Prior to version 1.8.223, an unauthenticated attacker can inject messages into any existing support conversation by sending a single email to the helpdesk's public address with a crafted In-Reply-To header. No…
When was CVE-2026-53591 disclosed?
CVE-2026-53591 was first published in the National Vulnerability Database on July 20, 2026, with the most recent update on July 21, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-53591 actively exploited?
CVE-2026-53591 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 87.9% of all scored CVEs.
What is the CVSS score of CVE-2026-53591?
CVE-2026-53591 has a CVSS v3 base score of 8.6 (NVD).
How do I remediate CVE-2026-53591?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-53591, 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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