Request smuggling via permissive chunk-size parsing
Published Jul 24, 2026 · Updated Jul 24, 2026
HTTP request smuggling in libsoup on Red Hat Enterprise Linux 6 through 10 allows remote attackers to bypass strict frontend parsing. soup_body_input_stream_read_chunked() passes chunk sizes to a permissive parser that accepts leading whitespace, plus signs, and invalid trailing characters forbidden by RFC 9112. Exploitation requires a strict frontend proxy to reject or delimit the same input differently, allowing a hidden request to reach the libsoup backend.
Summary
What happened
HTTP request smuggling in libsoup on Red Hat Enterprise Linux 6 through 10 allows remote attackers to bypass strict frontend parsing. soup_body_input_stream_read_chunked() passes chunk sizes to a permissive parser that accepts leading whitespace, plus signs, and invalid trailing characters forbidden by RFC 9112. Exploitation requires a strict frontend proxy to reject or delimit the same input differently, allowing a hidden request to reach the libsoup backend.
The record
- CVE
- CVE-2026-66338
- Published
- Jul 24, 2026
- Updated
- Jul 24, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat Enterprise Linux 6
- Classifications
- CWE-444, CAPEC-33, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 24, 2026CVE publishedPublication date reported by the CVE source.
- Jul 24, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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