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NVD / CVE Program· CNA redhat

CVE-2026-66337: Libsoup: libsoup: heap buffer over-read via integer underflow in soup_filter_input_stream_read_until()

Noroxi assessment

Priority: Monitor (action score 26/100)

  • 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 3.4.4-17 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 3.4.4-17 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 libsoup. An unsigned integer underflow in the soup_filter_input_stream_read_until() function causes a heap buffer over-read when parsing multipart HTTP responses. A malicious HTTP server can exploit this by sending a crafted multipart response, potentially causing the client application to crash or disclose sensitive heap memory.

MediumCVSS 6.5 · v3.1—No exploit Fix available
Published
Jul 24, 2026
Updated
Aug 24, 2026
EPSS
0.2% · 15th percentile

Report tools

JSON

Action score

26

Monitor

Low priority for now.

CVSS
26 / 40 · 6.5 / 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
6.5
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.

Get told when this record changes

  • 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.

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When you'll hear from us

  • when it enters CISA KEV
  • 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.

VendorProduct
gnomelibsoup
redhatenterprise linux

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • gnome libsoupall versions
  • redhat enterprise linux10.0
  • redhat enterprise linux6.0
  • redhat enterprise linux7.0
  • redhat enterprise linux8.0
  • redhat enterprise linux9.0

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 versionsaffected

  • 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—
Debian:14libsoup3before 3.8.0-13.8.0-1

Same product

gnome: all records

Other highest-scoring records for the same primary product.

  • CVE-2017-2885An exploitable stack based buffer overflow vulnerability exists in the GNOME libsoup 2.58.
    46Plan
  • CVE-2019-17266libsoup from versions 2.65.1 until 2.68.1 have a heap-based buffer over-read because soup_ntlm_parse_challenge() in soup-auth-ntlm.c does no
    40Plan
  • CVE-2018-12910The get_cookies function in soup-cookie-jar.c in libsoup 2.63.2 allows attackers to have unspecified impact via an empty hostname.
    40Plan

Published before and after this one in the same product

  • ← EarlierCVE-2026-2708Apr 23, 2026 · Libsoup: libsoup: http request smuggling via duplicate content-length headers
    21Monitor
  • ← EarlierCVE-2026-12548Jul 21, 2026 · Libsoup: heap out-of-bounds read in libsoup due to integer truncation
    16Monitor
  • Later →CVE-2026-66338Jul 24, 2026 · Libsoup: libsoup: http request smuggling via permissive chunk-size parsing in soup_body_input_stream_read_chunked()
    28Monitor

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 3.4.4-17 on Azure Linux 3.0Release NotesMicrosoft (MSRC)
debian:libsoup33.8.0-1 · Debian:14Package 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.

No dated events beyond publication.

EPSS, last 120 days

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

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

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-2026-10256067 days apartLibsoup: libsoup: heap buffer overflow during outgoing permessage-deflate buffer growth
    39Monitor
  • CVE-2026-10255767 days apartLibsoup: libsoup: heap buffer overflow during websocket message reassembly
    34Monitor
  • CVE-2026-10255867 days apartLibsoup: libsoup: heap buffer overflow during websocket receive-buffer growth
    34Monitor
  • CVE-2026-10255967 days apartLibsoup: libsoup: heap buffer overflow during websocket client-frame masking
    34Monitor
  • CVE-2026-10255567 days apartLibsoup: libsoup: heap buffer overflow via uninitialized length in data-uri base64 decoding
    32Monitor
  • CVE-2025-2784478 days apartLibsoup: heap buffer over-read in `skip_insignificant_space` when sniffing content
    26Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

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
low · data can be read
Integrity
none
Availability
low · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
Low
Integrity impact
None
Availability impact
Low

Weakness class (CWE)

CWE-125 · Out-of-bounds Read

CVSS vector

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

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✗ → ✓

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

References

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

All records