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NVD / CVE Program· CNA EEF

CVE-2026-43968: CR Injection in SSE Encoder Enables Event Splitting via cow_sse:event/1

Noroxi assessment

Priority: Monitor (action score 25/100)

  • 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: 0.26% (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.
  • Fixed version: ninenines cowlib 2.16.1, 6165fc40efa159ba1cceee7e7981e790acba5d9c; azl3 rabbitmq-server 3.13.7-3 on Azure Linux 3.0 3.13.7-4; azl3 rabbitmq-server 3.13.7-5 on Azure Linux 3.0 3.13.7-5.

Low priority for now. Upgrade to ninenines cowlib 2.16.1, 6165fc40efa159ba1cceee7e7981e790acba5d9c; azl3 rabbitmq-server 3.13.7-3 on Azure Linux 3.0 3.13.7-4; azl3 rabbitmq-server 3.13.7-5 on Azure Linux 3.0 3.13.7-5 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

Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE event splitting and injection via unvalidated field values. cow_sse:event/1 in cowlib guards the id and event fields against \n but not against bare \r, and the internal prefix_lines/2 function used for data and comment fields splits only on \n. Because the SSE specification requires decoders to treat \r\n, \r, and \n as equivalent line terminators, an attacker who controls any of these fields can inject additional SSE lines and forge a complete event with an arbitrary event type and data payload on the receiving end. In typical deployments where browser EventSource clients or other SSE consumers dispatch on event.type and render event.data, this enables event splitting, client-side logic manipulation, and stored-XSS-equivalent behaviour when event data is inserted into the DOM. This issue affects cowlib from 2.6.0 before 2.16.1.

MediumCVSS 6.3 · v4.0—No exploit Fix available
Published
May 11, 2026
Updated
Oct 26, 2026
EPSS
0.2% · 18th percentile

Report tools

JSON

Action score

25

Monitor

Low priority for now.

CVSS
25 / 40 · 6.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · EEF
6.3
NVD has not scored this yet; the score shown is the CNA’s.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N

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
nineninescowlib

Affected versions

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

  • ninenines cowlib2.6.0 and later · before 2.16.1

Versions reported by the vendor

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

  • ninenines cowlib

    • 2.6.0 and later · before 2.16.1affected · semver
    • 93b2b897cde238506c803faad4d1602d79dba7c9 and later · before 6165fc40efa159ba1cceee7e7981e790acba5d9caffected · git

Package-level exposure

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

EcosystemPackageAffected rangeFix
Hexcowlibfrom 2.6.0 · before 2.16.12.16.1

Same product

ninenines: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-59248Unbounded HPACK/QPACK prefixed-integer decoding in Cowlib causes memory-exhaustion DoS
    34Monitor
  • CVE-2026-7790Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS
    34Monitor
  • CVE-2026-43970Decompression Bomb in cow_spdy:inflate/2 Allows Memory Exhaustion via Crafted SPDY Frame
    32Monitor

Published before and after this one in the same product

  • Later →CVE-2026-43969May 11, 2026 · Cookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1
    8Monitor
  • Later →CVE-2026-43966Jun 8, 2026 · HTTP Response Splitting via Non-VCHAR Bytes in cow_http_struct_hd:escape_string/2
    25Monitor
  • Later →CVE-2026-43971Aug 18, 2026 · Link Header Directive Smuggling via Unescaped target/rel/Attribute Keys in cow_link:link/1
    25Monitor

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
ninenines cowlib2.16.1Vendor (CNA)
ninenines cowlib6165fc40efa159ba1cceee7e7981e790acba5d9cVendor (CNA)
azl3 rabbitmq-server 3.13.7-3 on Azure Linux 3.03.13.7-4 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 rabbitmq-server 3.13.7-5 on Azure Linux 3.03.13.7-5 · CBL-Mariner ReleasesMicrosoft (MSRC)
Hex:cowlib2.16.1Package 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.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

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

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-2026-439690 days apartCookie Request Header Injection via Unvalidated Encoder in cow_cookie:cookie/1
    8Monitor

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
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-93 · Improper Neutralization of CRLF Sequences ('CRLF Injection')

CVSS vector

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

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✗ → ✓

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References

Show all references (2 more)

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

All records