Request smuggling in Squid HTTP Transfer-Encoding handling
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · High · None
- Fix status
- Partial Red Hat: 5 without a fix
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.
Summary
Squid from 3.3.0.1 before 7.6 is affected. Its HTTP header parser accepts the bare Transfer-Encoding identity form, which HTTP prohibits, so requests can be interpreted differently (CWE-444). A trusted remote client with low privileges can smuggle requests over HTTP/1.1, bypassing protections placed between the attacker and Squid. When an HTTP cache runs in front of Squid, the attacker can also poison that cache with arbitrary content.
Written with Claude Haiku 5.5 from the sources below · 2026-10-27
Description from the CNA
Squid is a caching proxy for the Web. From 3.3.0.1 to before 7.6, due to an improper enforcement of behavioral workflow bug, Squid is vulnerable to a Request Smuggling attack against HTTP/1.1 Transfer-Encoding. HTTP header parsing (`src/HttpHeader.cc`) accepted the bare` Transfer-Encoding:` identity form, which the HTTP specification prohibits because any transfer coding must be wrapped within chunked encoding. This problem allows a trusted client to perform an HTTP Request Smuggling attack when HTTP/1.1 is used, bypassing security mechanisms that may be in place between attacker and Squid. When there is an HTTP cache operating prior to the affected Squid, this Request Smuggling attack also allows the attacker to poison that web cache and store arbitrary malicious content at any URL for delivery to other clients' future requests. This issue is fixed in version 7.6.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| squid-cache | squid | 3.3.0.1 to before 7.6 | 7.6 | Patch available | CNA |
- squid Vendorsquid-cache Affected 3.3.0.1 to before 7.6 Fixed in 7.6 Patch available CNA
CPE names Threatist (inferred) · 1
Inferred from how NVD named this product before; not given by a source.
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:* | — | — | squid-cache |
- cpe:2.3:a:squid-cache:squid:*:*:*:*:*:*:*:* Versions — — ·squid-cache
Remediation
Upgrade Squid to version 7.6 or later. Red Hat Enterprise Linux 6, 7, 8, 9 and 10 are listed as affected, with a fix plan of none available.
Written with Claude Haiku 5.5 from the sources below · 2026-10-27
- Fix · CNA squid (squid-cache) Fixed in 7.6
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 10 | Affected | No fix yet |
| Red Hat Enterprise Linux 6 | Affected | No fix yet |
| Red Hat Enterprise Linux 7 | Affected | No fix yet |
| Red Hat Enterprise Linux 8 | Affected | No fix yet |
| Red Hat Enterprise Linux 9 | Affected | No fix yet |
Timeline
- 2026-10-13 Threatist record created from CVE-2026-61642
- 2026-10-14 Priority changed: LOW → MEDIUM
- 2026-10-25 EPSS moved to the 50th–90th percentile
- 2026-10-25 Priority changed: MEDIUM → LOW
References
Other 6
- https://github.com/squid-cache/squid/security/advisories/GHSA-537g-4gfh-w7m6
- https://github.com/squid-cache/squid/pull/2427
- https://github.com/squid-cache/squid/pull/2431
- https://github.com/squid-cache/squid/commit/d06f48de8b8cc9a378cb91ecfe8e89b6e81696d2
- https://github.com/squid-cache/squid/commit/d808a7c825a70275113790471135c9c4d547ee51
- https://github.com/squid-cache/squid/releases/tag/SQUID_7_6
More squid-cache vulnerabilities
- TI-2025-38486 Squid vulnerable to information disclosure via authentication credential leakage in error handling CVSS 3.1CRITICAL 10.0
- TI-2024-16845 Denial of Service in HTTP Header parser in squid proxy CVSS 3.1HIGH 7.5
- TI-2024-16566 SQUID-2024:1 Denial of Service in HTTP Chunked Decoding CVSS 3.1HIGH 8.6
- TI-2023-26921 Denial of Service in HTTP Message Processing in Squid CVSS 3.1HIGH 8.6
- TI-2023-27496 SQUID-2023:10 Denial of Service in HTTP Request parsing CVSS 3.1HIGH 8.6
- TI-2023-25306 Squid: denial of service in http digest authentication CVSS 3.1HIGH 8.6
Sources
- CVE-2026-61642 · CVE Program
- CVE-2026-61642 · NVD
- FIRST EPSS
- CVE-2026-61642 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences