VulnerabilityPublished 30 Sep 2026Updated 5 Nov 2026

CVE-2026-103399: Red Hat Enterprise Linux 10 · Inconsistent Interpretation of HTTP Requests

Affects Red Hat Enterprise Linux 10Source CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium.

Data as of 14 Nov 2026, 20:43 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (redhat)	CVSS 3.1	5.3

EPSS: 0.2% chance of exploitation in 30 days – higher than 15% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 30 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 14 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Red Hat Enterprise Linux 10libsoup3	Affected–	Fixed in–
Red Hat Enterprise Linux 6libsoup	Affected–	Fixed in–
Red Hat Enterprise Linux 7libsoup	Affected–	Fixed in–
Red Hat Enterprise Linux 8libsoup	Affected–	Fixed in–
Red Hat Enterprise Linux 9libsoup	Affected–	Fixed in–

AI-suggested

Red Hat advises not to expose SoupServer to untrusted networks and to prefer terminating proxies or internal-only listeners. If SoupServer must be behind a reverse proxy, disable backend connection reuse or pooling across clients to prevent undrained bodies from being interpreted as new requests.

Description

CVE-2026-103399 is a moderate-impact HTTP/1 request smuggling vulnerability in SoupServer (libsoup) used in Red Hat Enterprise Linux 10. It occurs when an HTTP/1.x client sends a request with Expect: 100-continue and a request body, and the server sends an early final response before reading the body. The server fails to drain the body bytes or close the connection, causing leftover bytes to be interpreted as a new HTTP request on a keep-alive connection. This can lead to unintended request handling by processing a smuggled request.

Impact

An attacker can cause SoupServer to process a smuggled HTTP request by placing it in the body of an Expect: 100-continue request that is prematurely finalized by the server. This can lead to unintended request handling and potential integrity impacts. The vulnerability does not affect confidentiality or availability. The typical use of SoupServer for internal or development purposes limits the overall impact. Exploitation requires specific network configurations such as a reverse proxy that reuses backend connections across clients.

Summary

The vulnerability in SoupServer arises from inconsistent handling of HTTP/1.x requests with the Expect: 100-continue header. When the server returns a final non-1xx response before consuming the request body, it neither drains the body nor closes the connection. On persistent connections, leftover body bytes are misinterpreted as a subsequent HTTP request, enabling a remote unauthenticated attacker to smuggle a complete HTTP request. This violates HTTP/1.1 message framing as defined in RFC 9112. The impact is limited due to typical SoupServer deployment scenarios, which are mostly internal or development use rather than internet-facing. Exploitation involving cross-client request smuggling requires a reverse proxy that reuses backend connections across clients, which is not common in Red Hat deployments.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Nov 2026, 14:38 UTC

Technical details

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