CVE-2026-103399

MEDIUMPre-NVD 5.35.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

Score 5.3 from GitHub Security Advisory (severity: MODERATE) published 2026-09-30. A secondary CVSS source baseline 5.3; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: EPSS, GitHub Security Advisory, a secondary CVSS source

Also known asEUVD-2026-90226 (ENISA EUVD) · GHSA-mfgq-q7gx-p678 (GitHub Security Advisories)Source: ENISA EUVD

5.3EG
EchelonGraph verdictMonitorRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 5.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

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.

CVSS v3
5.3
EG Score
5.3MEDIUMmedium confidence
EG Risk
39
EG Risk 39/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity53% × 45%
Impact severity (EG Severity): CVSS 5.3 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation0.2% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Attend at high (mission-essential systems).
Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.2%
EPSS %ILE
15th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (5.3): severity, escalated by confirmed exploitation. This CVE's 5.3 is its impact severity (EG Severity), not escalated.

EG Severity
5.3 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-04). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Track at medium mission impactTrack at low or medium mission impact; Attend at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; 60 days if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Attend at high (mission-essential systems).

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation none (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; 60 days if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

September 30, 2026

Last Modified

November 5, 2026

Advisory Details (2)

Auto-updated Sep 30, 2026
Patch available. Sources: redhat.
Red Hat

2543949 – (CVE-2026-103399) CVE-2026-103399 libsoup: SoupServer: HTTP/1 request smuggling via undrained Expect: 100-continue body

https://bugzilla.redhat.com/show_bug.cgi?id=2543949
Red HatMentions a patch (unverified)

CVE-2026-103399 - Red Hat Customer Portal

Affected: Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to a

https://access.redhat.com/security/cve/CVE-2026-103399

Vendor Advisories for CVE-2026-103399(2)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(5 across 3 ecosystems)
Debian:12(2)
PackageVulnerable rangeFix by version rangeDependents
libsoup2.42.74.3-1 ... 2.74.3-9 (16 versions)
  • every version on: no fix on record
—
libsoup33.2.2-2 ... 3.8.0-3 (38 versions)
  • every version on: no fix on record
—
Debian:13(2)
PackageVulnerable rangeFix by version rangeDependents
libsoup2.42.74.3-10.1, 2.74.3-11
  • every version on: no fix on record
—
libsoup33.6.5-3 ... 3.8.0-3 (11 versions)
  • every version on: no fix on record
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
libsoup33.6.5-3 ... 3.6.6-1 (8 versions)
  • every version on: no fix on record
—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 6× in last 7d / 39× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed its CVE.org record (CNA or CISA ADP). An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). "EchelonGraph re-scored" is our own recompute of this CVE's score, not an update from a source, and is not counted in the refreshes above. Most recent first.

  1. 2026-11-13 16:50 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  2. 2026-11-12 16:32 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  3. 2026-11-11 16:37 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  4. 2026-11-10 16:41 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  5. 2026-11-09 16:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  6. 2026-11-08 16:37 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  7. 2026-11-06 16:35 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  8. 2026-11-05 16:36 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  9. 2026-11-05 16:28 UTCEchelonGraph re-scored
  10. 2026-11-05 16:28 UTCVendor advisory
  11. 2026-11-05 16:28 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub severity MODERATE · GitHub CVSS 5.3
  12. 2026-11-05 15:59 UTCEchelonGraph re-scored
  13. 2026-11-05 15:59 UTCVendor advisory
  14. 2026-11-05 15:59 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub severity MODERATE · GitHub CVSS 5.3
  15. 2026-11-04 16:34 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  16. 2026-11-03 16:45 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  17. 2026-11-03 02:17 UTCEchelonGraph re-scored
  18. 2026-11-03 02:17 UTCVendor advisory
  19. 2026-11-03 02:17 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub severity MODERATE · GitHub CVSS 5.3
  20. 2026-11-02 16:43 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  21. 2026-11-01 16:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  22. 2026-10-31 16:31 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  23. 2026-10-30 18:37 UTCEchelonGraph re-scored
  24. 2026-10-30 18:37 UTCVendor advisory
  25. 2026-10-30 18:37 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
Show 73 more
  1. 2026-10-30 16:33 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  2. 2026-10-29 16:32 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  3. 2026-10-28 16:31 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  4. 2026-10-27 16:31 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  5. 2026-10-26 16:30 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  6. 2026-10-25 16:32 UTCEPSS rescoreEPSS 0.2% · 15th percentile
  7. 2026-10-25 14:56 UTCEchelonGraph re-scored
  8. 2026-10-24 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  9. 2026-10-23 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  10. 2026-10-23 09:20 UTCEchelonGraph re-scored
  11. 2026-10-23 09:20 UTCVendor advisory
  12. 2026-10-23 09:20 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  13. 2026-10-22 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  14. 2026-10-21 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  15. 2026-10-20 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  16. 2026-10-19 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  17. 2026-10-18 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  18. 2026-10-18 05:09 UTCEchelonGraph re-scored
  19. 2026-10-17 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  20. 2026-10-16 16:40 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  21. 2026-10-15 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  22. 2026-10-14 16:31 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  23. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  24. 2026-10-12 16:40 UTCEchelonGraph re-scored
  25. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  26. 2026-10-11 22:26 UTCVendor advisory
  27. 2026-10-11 22:26 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  28. 2026-10-11 20:15 UTCEchelonGraph re-scored
  29. 2026-10-11 18:28 UTCEchelonGraph re-scored
  30. 2026-10-11 15:01 UTCEchelonGraph re-scored
  31. 2026-10-11 13:47 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  32. 2026-10-11 00:15 UTCEchelonGraph re-scored
  33. 2026-10-11 00:15 UTCVendor advisory
  34. 2026-10-11 00:14 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  35. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  36. 2026-10-10 02:01 UTCEchelonGraph re-scored
  37. 2026-10-10 02:01 UTCVendor advisory
  38. 2026-10-10 02:01 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  39. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  40. 2026-10-09 03:51 UTCEchelonGraph re-scored
  41. 2026-10-09 03:51 UTCVendor advisory
  42. 2026-10-09 03:50 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  43. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  44. 2026-10-08 05:41 UTCEchelonGraph re-scored
  45. 2026-10-08 05:41 UTCVendor advisory
  46. 2026-10-08 05:41 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  47. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  48. 2026-10-07 07:32 UTCEchelonGraph re-scored
  49. 2026-10-07 07:32 UTCVendor advisory
  50. 2026-10-07 07:32 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  51. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  52. 2026-10-06 09:23 UTCEchelonGraph re-scored
  53. 2026-10-06 09:23 UTCVendor advisory
  54. 2026-10-06 09:23 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  55. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  56. 2026-10-05 11:14 UTCEchelonGraph re-scored
  57. 2026-10-05 11:13 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  58. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  59. 2026-10-04 13:04 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  60. 2026-10-03 14:52 UTCEchelonGraph re-scored
  61. 2026-10-03 14:52 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  62. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.2% · 14th percentile
  63. 2026-10-02 16:43 UTCEchelonGraph re-scored
  64. 2026-10-02 16:43 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  65. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  66. 2026-10-01 18:33 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  67. 2026-09-30 20:22 UTCEchelonGraph re-scored
  68. 2026-09-30 20:22 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  69. 2026-09-30 19:12 UTCEchelonGraph re-scored
  70. 2026-09-30 19:11 UTCGHSA enrichmentGHSA-mfgq-q7gx-p678 · GitHub CVSS 5.3
  71. 2026-09-30 18:25 UTCEchelonGraph re-scored
  72. 2026-09-30 17:46 UTCEchelonGraph re-scoredFirst assessed: 5.3 MEDIUM
  73. 2026-09-30 17:45 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-103399?
CVE-2026-103399 is a medium-severity vulnerability; its CVE record was published on September 30, 2026. 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…
When was CVE-2026-103399 made public?
CVE-2026-103399 was made public on September 29, 2026: that is the date its CVE record's CNA, Red Hat, Inc., gives for when the vulnerability was made public. The CVE record itself was published on September 30, 2026. EchelonGraph's copy of the record carries a last-modified date of November 5, 2026; the record at its source may have been updated since.
Is CVE-2026-103399 actively exploited?
CVE-2026-103399 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.2% probability of exploitation in the next 30 days (15th percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-103399?
CVE-2026-103399 has a CVSS base score of 5.3 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-103399?
A fix for CVE-2026-103399 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-103399 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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