CVE-2026-66338: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in Red Hat Red Hat Enterprise Linux 10
A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.
AI Analysis
Technical Summary
CVE-2026-66338 is a medium severity vulnerability affecting Red Hat Enterprise Linux 10 via a flaw in libsoup. The chunked transfer encoding parser in libsoup uses a permissive parsing function for chunk sizes, accepting inputs that violate RFC 9112, such as leading whitespace, plus sign prefixes, and trailing invalid characters. This discrepancy between libsoup's parsing and that of strict frontend proxies can be exploited to smuggle HTTP requests, potentially leading to request desynchronization.
Potential Impact
The vulnerability allows an attacker to exploit differences in HTTP request parsing between libsoup and strict frontend proxies, enabling HTTP request/response smuggling. This can lead to partial bypass of security controls, request hijacking, or other unintended behaviors. The CVSS 3.1 base score is 5.4 (medium), reflecting limited confidentiality and integrity impact and no availability impact.
Mitigation Recommendations
Patch status is not yet confirmed — check the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-66338 for current remediation guidance. No official fix or workaround is explicitly stated in the advisory content provided.
CVE-2026-66338: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') in Red Hat Red Hat Enterprise Linux 10
Description
A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.
CVSS v3.1
Score 5.4medium
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
CVE-2026-66338 is a medium severity vulnerability affecting Red Hat Enterprise Linux 10 via a flaw in libsoup. The chunked transfer encoding parser in libsoup uses a permissive parsing function for chunk sizes, accepting inputs that violate RFC 9112, such as leading whitespace, plus sign prefixes, and trailing invalid characters. This discrepancy between libsoup's parsing and that of strict frontend proxies can be exploited to smuggle HTTP requests, potentially leading to request desynchronization.
Potential Impact
The vulnerability allows an attacker to exploit differences in HTTP request parsing between libsoup and strict frontend proxies, enabling HTTP request/response smuggling. This can lead to partial bypass of security controls, request hijacking, or other unintended behaviors. The CVSS 3.1 base score is 5.4 (medium), reflecting limited confidentiality and integrity impact and no availability impact.
Mitigation Recommendations
Patch status is not yet confirmed — check the Red Hat advisory at https://access.redhat.com/security/cve/CVE-2026-66338 for current remediation guidance. No official fix or workaround is explicitly stated in the advisory content provided.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- redhat
- Date Reserved
- 2026-07-24T22:32:18.748Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
- Vendor Advisory Urls
- [{"url":"https://access.redhat.com/security/cve/CVE-2026-66338","vendor":"Red Hat"}]
Threat ID: 6a63f3c69c2644c7f8bc9752
Added to database: 07/24/2026, 23:22:46 UTC
Last enriched: 08/01/2026, 21:02:26 UTC
Last updated: 09/07/2026, 12:52:30 UTC
Views: 108
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