When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a "Trailer" header that declares a large number of fields, causing the server to allocate a disproportionate amount of memory while bypassing Server.MaxHeaderValueCount and Server.MaxHeaderBytes limits. This exploit is not applicable for HTTP/1 servers, which do not support multiplexing a large number of requests over one TCP connection, and whose Server.MaxHeaderBytes are calculated differently.
CVE-2026-78659
HIGHPre-NVD 7.57.5Trending — 4 sources updated this week
EchelonGraph scoreLOW confidence
This high-severity CVE scores 7.5 under CISA-ADP (Vulnrichment) CVSS v3.1 (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). 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: cisa-adp
7.5EG
EchelonGraph verdictPlan mitigationSerious severity, but no confirmed exploitation yet.
- High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 7.5Exploit: None knownExposed services: Not assessed
No fix is confirmed yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for the fix.
- CVSS v3
- 7.5
- EG Score
- 7.5HIGHlow confidence
- EG Risk
- 49EG Risk 49/100CISA SSVC
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 computedSeverity75% × 45%Exploitation0% × 40%Automatability100% × 15%CISA SSVC: Track at low or medium mission impact; Attend at high (mission-essential systems).Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix. - EPSS PROB
- 0.2%
- EPSS %ILE
- 12th
- KEV
- Not listed
CISA SSVCTrack at low or medium mission impact; Attend at high (mission-essential systems).
No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines at low or medium mission impact and sooner than that at high, and watch the vendor's advisory for the fix.
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Mission impact is CISA's Mission & Well-being decision point, and only you can judge it: high means the affected system is essential to your organisation's mission, or its compromise could cause irreversible harm to people. CISA's decision table
Published
October 8, 2026
Last Modified
October 9, 2026
Advisory Details (6)
Auto-updated Oct 9, 2026No fix on record yet.
generic
generic
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 6× in last 7d / 6× 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.
- 2026-10-09 20:07 UTCEPSS rescore
- 2026-10-09 15:39 UTCEG score recompute▲ 7.50
- 2026-10-09 15:38 UTCMITRE cvelistV5CVSS v3 → 7.5 · severity → HIGH
- 2026-10-08 23:20 UTCNVD update
- 2026-10-08 22:58 UTCEG score recompute
- 2026-10-08 22:58 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-78659?
CVE-2026-78659 is a high vulnerability published on October 8, 2026. When "Trailer" headers are sent by a client, the HTTP server internally uses the header values to populate the Request.Trailer map passed to the server handler. Because Request.Trailer is a map, each entry incurs memory overhead. For HTTP/2 servers, a malicious client can exploit this by sending a…
When was CVE-2026-78659 disclosed?
CVE-2026-78659 was first published on October 8, 2026, with the most recent update on October 9, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-78659 actively exploited?
CVE-2026-78659 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (12th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-78659?
CVE-2026-78659 has a CVSS v3.1 base score of 7.5 (CISA-ADP / Vulnrichment enrichment; NVD's own analysis pending). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-78659?
No fix for CVE-2026-78659 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-78659
Is Your Infrastructure Affected by CVE-2026-78659?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.