In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, front-end request desynchronization is possible in the proxy request forwarding component. A request that contains both a Content-Length and a Transfer-Encoding header is forwarded with both headers present, while Fiddler frames the body using Transfer-Encoding only. The remaining bytes on the reused client connection are then parsed as a separate pipelined request, so a local threat actor with low privileges can cause a single malformed request to be split into two requests forwarded to the origin server and receive an additional smuggled response, without requiring a vulnerable server.
CVE-2026-77803
LOWPre-NVD 3.63.6Trending — 4 sources updated this week
EchelonGraph scoreHIGH confidence
“—” beside the score: it is equal to the CVSS score beside it.
Score 3.6 from GitHub Security Advisory (severity: LOW) published 2026-10-05. A secondary CVSS source baseline 3.6; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source
3.6EG
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: 3.6Exploit: 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
- 3.6
- EG Score
- 3.6LOWhigh confidence
- EG Risk
- 16EG Risk 16/100
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)Severity36% × 45%The EG Score, 3.6 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 every mission impact level.Exploitation none (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: 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 every mission impact level.
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 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
October 5, 2026
Last Modified
October 6, 2026
References (1)
Vendor Advisories for CVE-2026-77803(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 20× in last 7d / 20× 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.
- 2026-10-11 19:23 UTCEG score recompute
- 2026-10-11 16:39 UTCEG score recompute
- 2026-10-11 13:57 UTCEG score recompute
- 2026-10-11 13:49 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
- 2026-10-10 20:00 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
- 2026-10-09 20:07 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
- 2026-10-09 13:48 UTCEG score recompute
- 2026-10-09 13:48 UTCGHSA enrichmentGHSA-xq67-hr2w-mm32 · GitHub severity LOW · GitHub CVSS 3.6
- 2026-10-08 17:13 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
- 2026-10-07 23:48 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
- 2026-10-06 18:33 UTCEG score recompute
- 2026-10-06 18:33 UTCGHSA enrichmentGHSA-xq67-hr2w-mm32 · GitHub severity LOW · GitHub CVSS 3.6
- 2026-10-06 17:57 UTCEG score recompute
- 2026-10-06 17:57 UTCGHSA enrichmentGHSA-xq67-hr2w-mm32 · GitHub severity LOW · GitHub CVSS 3.6
- 2026-10-06 15:25 UTCEG score recompute
- 2026-10-06 15:25 UTCGHSA enrichmentGHSA-xq67-hr2w-mm32 · GitHub severity LOW · GitHub CVSS 3.6
- 2026-10-06 15:18 UTCEPSS rescoreEPSS <0.1% · below the 1st percentile
- 2026-10-05 13:18 UTCEG score recompute
- 2026-10-05 13:02 UTCEG score recomputeFirst assessed: 3.6 LOW
- 2026-10-05 13:01 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-77803?
CVE-2026-77803 is a low-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, front-end request desynchronization is possible in the proxy request forwarding component. A request that contains both a Content-Length and a Transfer-Encoding header is forwarded with both headers present,…
When was the CVE record for CVE-2026-77803 published?
The CVE record for CVE-2026-77803 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-2026-77803 actively exploited?
CVE-2026-77803 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-2026-77803?
CVE-2026-77803 has a CVSS base score of 3.6 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-77803?
No fix for CVE-2026-77803 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-2026-77803 are linked in the Vendor Advisories panel on this page.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-77803
Is Your Infrastructure Affected by CVE-2026-77803?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.