CVE-2026-43968: Improper Neutralization of CRLF Sequences ('CRLF Injection') vulnerability in ninenines cowlib allows SSE even

Routine

MEDIUM 4.0REMOTEUPGRADE

CVE-2026-43968 is a medium-severity flaw (CVSS 4.0) affecting cowlib. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 term

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	4.0 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 82%)
CISA exploited list	No
Weakness	CWE-93
Published	2026-05-11
Last modified	2026-10-26

Publisher (CNA): EEF · Vendor: ninenines

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-11 19:16 UTCPublished CVE record published
2026-10-26 18:10 UTCUpdated Record last modified

ninenines cowlib UPGRADE

Affected: >= 2.6.0 and < 2.16.1

Fixed in: 2.16.1

Safe to downgrade to: a release before 2.6.0

1. Check installed version

apt-cache policy cowlib || rpm -q cowlib || cowlib --version

2. UPGRADE to 2.16.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade cowlib

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade cowlib

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.6.0 (Debian / Ubuntu)

apt-cache madison cowlib sudo apt install cowlib=<VERSION_BEFORE_2.6.0> sudo apt-mark hold cowlib

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list cowlib sudo dnf downgrade cowlib-<VERSION_BEFORE_2.6.0> sudo dnf versionlock add cowlib

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-43968?

cowlib: upgrade to 2.16.1. Exact commands for each OS are on this page.

Is CVE-2026-43968 being exploited?

CVE-2026-43968 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-43968 affect?

CVE-2026-43968 affects cowlib. Severity is medium (CVSS 4.0). 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 n

How urgent is CVE-2026-43968?

Priority 24/100. Remotely exploitable, no login, no user action

Related CVEs

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CVE-2026-7790 HIGH 7.5 UPGRADE Uncontrolled Resource Consumption vulnerability in ninenines cowlib (cow_http_te module) allows Excessive Allo

References

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