CVE-2026-77802

MEDIUMPre-NVD 6.36.3
EchelonGraph scoreHIGH confidence

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

Score 6.3 from GitHub Security Advisory published 2026-10-05. A secondary CVSS source baseline 6.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
Trending — 4 sources updated this week
6.3EG
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: <0.1%CVSS: 6.3Exploit: None knownExposed services: Not assessed

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

In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, HTTP request smuggling is possible in the proxy request forwarding component. Requests containing multiple Content-Length headers with conflicting values are forwarded verbatim to the origin server, while Fiddler frames the request body using only the first Content-Length value. A local threat actor with low privileges who is able to send requests through the same Fiddler proxy instance as another user can exploit this desynchronization against a non-RFC-9110-compliant origin server that keeps the connection alive to smuggle an additional request. Because Fiddler returns the server connection to its pipe pool after reading only the first response, the unread smuggled response remains buffered on the socket and is served to the next session that reuses that connection, allowing the attacker to poison responses delivered to other users and to obtain responses intended for them.

CVSS v3
6.3
EG Score
6.3MEDIUMhigh confidence
EG Risk
28
EG Risk 28/100

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)
Severity63% × 45%
The EG Score, 6.3 of 10.
Exploitation<0.1% × 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 low or medium mission impact; Track* at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation within your standard update timelines, and watch the vendor's advisory for the fix.
EPSS PROB
<0.1%
EPSS %ILE
below the 1st
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* 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, and watch the vendor's advisory for the fix.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (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)14 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 total (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

October 5, 2026

Last Modified

October 6, 2026

Advisory Details (1)

Auto-updated Oct 5, 2026
No fix on record yet.
Web page

Fiddler Classic HTTP Request Smuggling Vulnerability (CVE-2026-77802) - Progress Telerik Fiddler Classic

https://docs.telerik.com/fiddler/knowledge-base/kb-security-http-request-smuggling-cve-2026-77802

Vendor Advisories for CVE-2026-77802(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 26× in last 7d / 26× 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. 2026-10-12 00:38 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  2. 2026-10-11 19:23 UTCEG score recompute
  3. 2026-10-11 16:39 UTCEG score recompute
  4. 2026-10-11 13:57 UTCEG score recompute
  5. 2026-10-11 13:49 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
  6. 2026-10-10 23:26 UTCEG score recompute
  7. 2026-10-10 23:26 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  8. 2026-10-10 20:00 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
  9. 2026-10-09 22:14 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  10. 2026-10-08 21:01 UTCEG score recompute
  11. 2026-10-08 21:01 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  12. 2026-10-08 17:13 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
  13. 2026-10-07 23:48 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
  14. 2026-10-07 19:46 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  15. 2026-10-06 18:33 UTCEG score recompute
  16. 2026-10-06 18:33 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  17. 2026-10-06 17:57 UTCEG score recompute
  18. 2026-10-06 17:57 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  19. 2026-10-06 15:25 UTCEG score recompute
  20. 2026-10-06 15:25 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  21. 2026-10-06 15:18 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
  22. 2026-10-06 14:32 UTCEG score recompute
  23. 2026-10-06 14:32 UTCGHSA enrichmentGHSA-p3gc-87rm-gmjp · GitHub CVSS 6.3
  24. 2026-10-05 13:18 UTCEG score recompute
  25. 2026-10-05 13:02 UTCEG score recomputeFirst assessed: 6.3 MEDIUM
Show 1 more
  1. 2026-10-05 13:01 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-77802?
CVE-2026-77802 is a medium-severity vulnerability; its CVE record was published on October 5, 2026. In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, HTTP request smuggling is possible in the proxy request forwarding component. Requests containing multiple Content-Length headers with conflicting values are forwarded verbatim to the origin server, while…
When was the CVE record for CVE-2026-77802 published?
The CVE record for CVE-2026-77802 was published on October 5, 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 October 6, 2026; the record at its source may have been updated since.
Is CVE-2026-77802 actively exploited?
CVE-2026-77802 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a <0.1% probability of exploitation in the next 30 days (below the 1st percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-77802?
CVE-2026-77802 has a CVSS base score of 6.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-77802?
No fix for CVE-2026-77802 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. The vendor advisories EchelonGraph has for CVE-2026-77802 are linked in the Vendor Advisories panel on this page.

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