How severe is CVE-2026-23991?

CVE-2026-23991 has a CVSS score of 5.9/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2026-23991?

CVE-2026-23991 affects the following packages: github.com/theupdateframework/go-tuf/v2 (Go). Ecosystems affected: Go.

How do I fix CVE-2026-23991?

Update github.com/theupdateframework/go-tuf/v2 to 2.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23991 is resolved across your whole dependency graph.

How do I detect CVE-2026-23991 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/theupdateframework/go-tuf/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-23991 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-23991 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-23991 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-23991?

CVE-2026-23991 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 48th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-23991?

CVE-2026-23991 is classified as Reachable Assertion (CWE-617), CWE-754 (CWE-754). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-23991 published, and has it been updated?

CVE-2026-23991 was published on January 22, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2026-23991 — go-tuf

MEDIUMFix: theupdateframework/go-tuf@73345ab

CVE-2026-23991 is a medium-severity (CVSS 5.9) Reachable Assertion vulnerability in github.com/theupdateframework/go-tuf/v2. A fix is available for github.com/theupdateframework/go-tuf/v2 — see the affected versions and patch details below.

go-tuf affected by client DoS via malformed server response

Also known asGHSA-846p-jg2w-w324GO-2026-4348

Published

Jan 22, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23991.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs48th percentile — riskier than 48% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/theupdateframework/go-tuf/v2

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Security Disclosure: Client DoS via malformed server response

Summary

If the TUF repository (or any of its mirrors) returns invalid TUF metadata JSON (valid JSON but not well formed TUF metadata), the client will panic during parsing, causing a DoS. The panic happens before any signature is validated. This means that a compromised repository/mirror/cache can DoS clients without having access to any signing key.

Impact

Client crashes upon receiving and parsing malformed TUF metadata. This can cause long running services to enter an restart/crash loop.

Workarounds

None currently.

Affected code

The metadata.checkType function did not properly type assert the (untrusted) input causing it to panic on malformed data.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/theupdateframework/go-tuf/v2`	all versions	2.3.1`go get github.com/theupdateframework/go-tuf/v2@v2.3.1`

Affected Products

1 product · 1 configurations

Application

go-tuftheupdateframework

≥ 2.0.0 && < 2.3.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/theupdateframework/go-tuf/v2, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/theupdateframework/go-tuf/v2 to 2.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23991 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

The state of a TUF repository/mirror/cache is outside the control of the attacker prior to compromise. Following documented Red Hat guidance for repository creation will ensure that these preconditions are not present.

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2026-23991 (CC BY 4.0)

Frequently Asked Questions

# Security Disclosure: Client DoS via malformed server response ## Summary If the TUF repository (or any of its mirrors) returns invalid TUF metadata JSON (valid JSON but not well formed TUF metadata), the client will panic _during parsing_, causing a DoS. The panic happens before any signature is validated. This means that a compromised repository/mirror/cache can DoS clients without having access to any signing key. ## Impact Client crashes upon receiving and parsing malformed TUF metadata. This can cause long running services to enter an restart/crash loop. ## Workarounds None curren