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CVE.org (no NVD analysis yet)· CNA redhat

CVE-2026-103399: Libsoup: soupserver: http/1 request smuggling via undrained expect: 100-continue body

MediumCVSS 5.3 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 21/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.24% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: azl3 libsoup 3.4.4-16 on Azure Linux 3.0 Release Notes; azl3 libsoup 3.4.4-18 on Azure Linux 3.0 Release Notes.

Low priority for now. Upgrade to azl3 libsoup 3.4.4-16 on Azure Linux 3.0 Release Notes; azl3 libsoup 3.4.4-18 on Azure Linux 3.0 Release Notes or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

A flaw was found in SoupServer (libsoup). When an HTTP/1.x client sends a request with Expect: 100-continue and a request body, and SoupServer returns an early final (non-1xx) response before the body is read, the server neither drains the declared body bytes nor closes the connection. On a keep-alive connection, those leftover bytes are interpreted as a subsequent HTTP request. A remote, unauthenticated attacker can place a complete HTTP request in the body and cause SoupServer to process that smuggled request, leading to unintended request handling.

Published
Sep 30, 2026
Updated
Nov 5, 2026
EPSS
0.2% · 15th percentile

Report tools

JSON

Action score

21

Monitor

Low priority for now.

CVSS
21 / 40 · 5.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · redhat
5.3
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-103399

When you'll hear from us

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  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (redhat). Independent of NVD's CPE analysis and usually ahead of it.

  • Red Hat Red Hat Enterprise Linux 10

    • all versionsaffected

  • Red Hat Red Hat Enterprise Linux 6

    • all versionsunknown

  • Red Hat Red Hat Enterprise Linux 7

    • all versionsaffected

  • Red Hat Red Hat Enterprise Linux 8

    • all versionsaffected

  • Red Hat Red Hat Enterprise Linux 9

    • all versionsaffected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12libsoup2.4from 0—
Debian:12libsoup3from 0—
openSUSE:Leap 16.0libsoupbefore 3.6.6-160000.5.13.6.6-160000.5.1
openSUSE:Tumbleweedlibsoup2before 2.74.3-25.12.74.3-25.1
SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOSlibsoupbefore 3.0.4-150400.3.58.13.0.4-150400.3.58.1
SUSE:Linux Enterprise Micro 5.3libsoup2before 2.74.3-150400.3.43.12.74.3-150400.3.43.1
SUSE:Linux Enterprise Module for Basesystem 15 SP7libsoupbefore 3.4.4-150600.3.62.13.4.4-150600.3.62.1
SUSE:Linux Enterprise Module for Basesystem 15 SP7libsoup2before 2.74.3-150600.4.42.12.74.3-150600.4.42.1
SUSE:Linux Enterprise Server 12 SP5-LTSSlibsoupbefore 2.62.2-5.49.12.62.2-5.49.1
SUSE:Linux Enterprise Server 16.0libsoupbefore 3.6.6-160000.5.13.6.6-160000.5.1
SUSE:Linux Micro 6.0libsoupbefore 3.4.2-159998.1.13.4.2-159998.1.1

Same product

red hat: all records

Other highest-scoring records for the same primary product.

  • CVE-2025-10230Samba: command injection in wins server hook script
    52Plan
  • CVE-2026-4631Cockpit: cockpit: unauthenticated remote code execution due to ssh command-line argument injection
    44Plan
  • CVE-2026-76578Ipa: freeipa: freeipa: unauthenticated ldap client can obtain administrator credentials via the self-managed-token aci
    39Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2026-95520Sep 29, 2026 · Rpm: rpm: integer overflow in iterreadarchivenext() leads to heap-based buffer overflow when parsing untrusted rpm packages
    28Monitor
  • ← EarlierCVE-2026-103242Sep 30, 2026 · Rpm: heap-based buffer overflow write in hex2binv() via a mistyped rpmtag_filesignatures header tag
    28Monitor
  • Later →CVE-2026-103641Oct 1, 2026 · Gegl: gegl04: gegl: out-of-bounds read in the radiance hdr uncompressed scanline decoder
    22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
azl3 libsoup 3.4.4-16 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
azl3 libsoup 3.4.4-18 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
debian:libsoup33.8.0-1 · Debian:14Package registry (OSV)
opensuse:libsoup3.6.6-160000.5.1 · openSUSE:Leap 16.0Package registry (OSV)
opensuse:libsoup22.74.3-25.1 · openSUSE:TumbleweedPackage registry (OSV)
suse:libsoup2.62.2-5.49.1 · SUSE:Linux Enterprise Server 12 SP5-LTSSPackage registry (OSV)
suse:libsoup3.4.2-159998.1.1 · SUSE:Linux Micro 6.0Package registry (OSV)
suse:libsoup22.74.3-150600.4.42.1 · SUSE:Linux Enterprise Module for Basesystem 15 SP7Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. Fix recorded+13 d
  3. TodayNov 13, 2026+44 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2025-14523293 days apartLibsoup: libsoup: duplicate host header handling causes host-parsing discrepancy (first- vs last-value wins)
    32Monitor
  • CVE-2026-1760240 days apartLibsoup: soupserver: denial of service via http request smuggling
    21Monitor
  • CVE-2026-6324124 days apartLibsoup: libsoup: http request smuggling via unsigned to signed conversion error
    19Monitor

Not on record for this CVE: patch commit or PR link · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
low · data or configuration can be modified
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
Low
Availability impact
None

Weakness class (CWE)

CWE-444 · Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓
  2. SSVC exploitation— → none
  3. Exploit maturity— → none

For records you follow, these changes also arrive as notifications. →

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records