# CVE-2026-72889: Net::OAuth versions before 0.33 for Perl allow the sender to choose the signature algorithm in verify

> Attackers can forge OAuth requests by choosing a weak signature algorithm, bypassing authentication checks in Net::OAuth Perl library.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Aug 2026
- **Updated:** 26 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-72889, GHSA-c8rm-g5cm-4pf5, UBUNTU-CVE-2026-72889

## What is CVE-2026-72889?

CVE-2026-72889 is a critical vulnerability, published on 19 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Net::OAuth versions before 0.33 for Perl allow the sender to choose the signature algorithm in verify.

verify resolves the signature method class from the signature_method parameter of the incoming message. signature_method is required on every request, so the algorithm used to check a signature is chosen by whoever sent it, and nothing lets the verifying party pin the method instead. When a message names HMAC-SHA1 or HMAC-SHA256, the key is derived from consumer_secret and token_secret rather than from the key the provider deployed.

A provider deployed on RSA-SHA1 holds only the consumer public key, and RFC 5849 does not use consumer_secret for that method, so the required parameter is filled with a placeholder. A client that names HMAC-SHA1 instead has its signature checked against that placeholder, so a guessable one is enough to forge requests for any consumer key and token.

Weakness: CWE-757 (Selection of Less-Secure Algorithm During Negotiation), CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-72889?


## How do I fix CVE-2026-72889?

Upgrade to a fixed version.

## Is CVE-2026-72889 being exploited?

There is no known exploitation of CVE-2026-72889 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72889 and fix it if it is affected.

What it is: CVE-2026-72889 is a critical vulnerability, published on 19 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-72889 in the wild and no public exploit code.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72889/ (Markdown: https://insights.sbomify.com/CVE-2026-72889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72889
- OSV: https://osv.dev/vulnerability/CVE-2026-72889

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72889/
Summaries are generated and may contain mistakes; the official description above is the record.