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8 vulnerabilities found for Progress® Telerik® Fiddler® Classic by Progress Software
CVE-2026-77805 (GCVE-0-2026-77805)
Vulnerability from nvd – Published: 2026-10-05 12:40 – Updated: 2026-10-05 15:26
VLAI
EPSS
VEX
Title
Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, the integrity check applied to the external helper tools launched by the application is insufficient. Before executing a helper tool, the application only verifies that the file carries a valid Authenticode signature whose certificate subject name matches a broad allow list of publisher name fragments, rather than verifying that the file is the specific executable shipped with that version of the product. A local threat actor with low privileges who replaces one of these helper executables with any other validly signed binary from an allow-listed publisher can cause the substituted binary to be executed by the application, including with Administrator privileges for the tools that request elevation, resulting in privilege escalation and execution of unintended code. Successful exploitation requires the user to launch the affected external tool and to approve the elevation prompt without noticing that it refers to a different executable.
Severity
7.9 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-05 15:25 UTC
CWE
- CWE-347 - Improper Verification of Cryptographic Signature
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
1.0.0 , < 6.0.20262.10021
(custom)
|
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CVE-2026-77804 (GCVE-0-2026-77804)
Vulnerability from nvd – Published: 2026-10-05 12:40 – Updated: 2026-10-06 17:49
VLAI
EPSS
VEX
Title
Time-of-check Time-of-use (TOCTOU) Race Condition in Root Certificate Installation in Progress® Telerik® Fiddler® Classic
Summary
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, a time-of-check time-of-use (TOCTOU) race condition exists in the installation of the HTTPS interception root certificate into the Local Computer certificate store. Fiddler writes the certificate to a temporary file in a user-writable location and then launches the external TrustCert helper application, which elevates and imports the certificate from that file. A local threat actor with low privileges who replaces the temporary file between the time it is written and the time the elevated helper reads it can cause an attacker-supplied root certificate to be installed in the Local Computer Trusted Root Certification Authorities store, enabling subsequent interception and modification of TLS-protected traffic on the machine. Successful exploitation requires the user to initiate the certificate trust operation and approve the elevation prompt.
Severity
6.6 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:49 UTC
CWE
- CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
1.0.0 , < 6.0.20262.10021
(custom)
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CVE-2026-77803 (GCVE-0-2026-77803)
Vulnerability from nvd – Published: 2026-10-05 12:39 – Updated: 2026-10-06 17:50
VLAI
EPSS
VEX
Title
Front-end Desynchronization Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
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.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:50 UTC
CWE
- CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
1.0.0 , < 6.0.20262.10021
(custom)
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CVE-2026-77802 (GCVE-0-2026-77802)
Vulnerability from nvd – Published: 2026-10-05 12:38 – Updated: 2026-10-06 17:51
VLAI
EPSS
VEX
Title
HTTP Request Smuggling Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
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.
Severity
6.3 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:50 UTC
CWE
- CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
1.0.0 , < 6.0.20262.10021
(custom)
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CVE-2026-77805 (GCVE-0-2026-77805)
Vulnerability from cvelistv5 – Published: 2026-10-05 12:40 – Updated: 2026-10-05 15:26
VLAI
EPSS
VEX
Title
Weak Executable Signature Verification Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, the integrity check applied to the external helper tools launched by the application is insufficient. Before executing a helper tool, the application only verifies that the file carries a valid Authenticode signature whose certificate subject name matches a broad allow list of publisher name fragments, rather than verifying that the file is the specific executable shipped with that version of the product. A local threat actor with low privileges who replaces one of these helper executables with any other validly signed binary from an allow-listed publisher can cause the substituted binary to be executed by the application, including with Administrator privileges for the tools that request elevation, resulting in privilege escalation and execution of unintended code. Successful exploitation requires the user to launch the affected external tool and to approve the elevation prompt without noticing that it refers to a different executable.
Severity
7.9 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-05 15:25 UTC
CWE
- CWE-347 - Improper Verification of Cryptographic Signature
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
1.0.0 , < 6.0.20262.10021
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CVE-2026-77804 (GCVE-0-2026-77804)
Vulnerability from cvelistv5 – Published: 2026-10-05 12:40 – Updated: 2026-10-06 17:49
VLAI
EPSS
VEX
Title
Time-of-check Time-of-use (TOCTOU) Race Condition in Root Certificate Installation in Progress® Telerik® Fiddler® Classic
Summary
In Progress® Telerik® Fiddler® Classic for Windows, versions prior to v6.0.20262.10021, a time-of-check time-of-use (TOCTOU) race condition exists in the installation of the HTTPS interception root certificate into the Local Computer certificate store. Fiddler writes the certificate to a temporary file in a user-writable location and then launches the external TrustCert helper application, which elevates and imports the certificate from that file. A local threat actor with low privileges who replaces the temporary file between the time it is written and the time the elevated helper reads it can cause an attacker-supplied root certificate to be installed in the Local Computer Trusted Root Certification Authorities store, enabling subsequent interception and modification of TLS-protected traffic on the machine. Successful exploitation requires the user to initiate the certificate trust operation and approve the elevation prompt.
Severity
6.6 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:49 UTC
CWE
- CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
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CVE-2026-77803 (GCVE-0-2026-77803)
Vulnerability from cvelistv5 – Published: 2026-10-05 12:39 – Updated: 2026-10-06 17:50
VLAI
EPSS
VEX
Title
Front-end Desynchronization Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
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.
Severity
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:50 UTC
CWE
- CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
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|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
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CVE-2026-77802 (GCVE-0-2026-77802)
Vulnerability from cvelistv5 – Published: 2026-10-05 12:38 – Updated: 2026-10-06 17:51
VLAI
EPSS
VEX
Title
HTTP Request Smuggling Vulnerability in Progress® Telerik® Fiddler® Classic
Summary
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.
Severity
6.3 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-10-06 17:50 UTC
CWE
- CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://docs.telerik.com/fiddler/knowledge-base/k… | vendor-advisory |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| Progress Software | Progress® Telerik® Fiddler® Classic |
Affected:
1.0.0 , < 6.0.20262.10021
(custom)
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