CVE-2026-123660: In Vulnerability-Lookup 5.5.1 up to but not including 6.4.1, a signed-in user could make the server allocate m

Routine

MEDIUM 5.3UPGRADE

CVE-2026-123660 is a medium-severity flaw (CVSS 5.3) affecting vulnerability-lookup. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In Vulnerability-Lookup 5.5.1 up to but not including 6.4.1, a signed-in user could make the server allocate memory far out of proportion to their input through a webhook notification's payload template. Each placeholder's format specifier was passed unchanged to Python's string formatting, which builds the padded result before its size can be checked. A template of a few dozen bytes, such as {"text": "{title:>999999999}"}, therefore produced a s

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
EPSS exploit chance	n/a
CISA exploited list	No
Weakness	CWE-770, CWE-1284, CWE-674
Published	2026-11-06
Last modified	2026-11-06

Publisher (CNA): CIRCL · Vendor: vulnerability-lookup · Source: CVE Program record (NVD analysis pending)

Last updated 2026-11-06 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-11-06 08:58 UTCPublished CVE record published
2026-11-06 09:04 UTCUpdated Record last modified

vulnerability-lookup vulnerability-lookup UPGRADE

Affected: >= 5.5.1 and < 6.4.1

Fixed in: 6.4.1

Safe to downgrade to: a release before 5.5.1

1. Check installed version

apt-cache policy vulnerability-lookup || rpm -q vulnerability-lookup || vulnerability-lookup --version

2. UPGRADE to 6.4.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade vulnerability-lookup

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade vulnerability-lookup

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 5.5.1 (Debian / Ubuntu)

apt-cache madison vulnerability-lookup sudo apt install vulnerability-lookup=<VERSION_BEFORE_5.5.1> sudo apt-mark hold vulnerability-lookup

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

dnf --showduplicates list vulnerability-lookup sudo dnf downgrade vulnerability-lookup-<VERSION_BEFORE_5.5.1> sudo dnf versionlock add vulnerability-lookup

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-2026-123660?

vulnerability-lookup: upgrade to 6.4.1. Exact commands for each OS are on this page.

Is CVE-2026-123660 being exploited?

CVE-2026-123660 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-2026-123660 affect?

CVE-2026-123660 affects vulnerability-lookup. Severity is medium (CVSS 5.3). In Vulnerability-Lookup 5.5.1 up to but not including 6.4.1, a signed-in user could make the server allocate memory far out of proportion to their input through a webhook notification's payload template. Each placeholder's format specifier

How urgent is CVE-2026-123660?

Priority 19/100. No elevated risk signals yet.

Software pages

Python vulnerabilities

References

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