# CVE-2026-77972: safeurl validated address is not bound to the request, allowing DNS rebinding

> An attacker can bypass SSRF protections in the safeurl library via DNS rebinding, allowing access to internal network resources.

- **Severity:** Critical 9.0 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:L/VA:N/SC:H/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Sep 2026
- **Updated:** 21 Sep 2026
- **Also known as:** EEF-CVE-2026-77972, GHSA-pqwh-q74p-w7h4

## What is CVE-2026-77972?

CVE-2026-77972 is a critical server-side request forgery vulnerability in Slab safeurl, published on 15 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Time-of-check Time-of-use (TOCTOU) Race Condition in Slab safeurl allows an attacker who controls a hostname's DNS responses to reach internal network destinations that validation rejected.

Validation returns a verdict and not the address it approved, so the HTTP clients the library ships receive the original hostname and resolve it a second time when the request is made. An attacker who controls the authoritative DNS for a name can answer the first lookup with a permitted address and the second with a blocked one, and the request then reaches a destination validation never approved. The same window opens without an attacker whenever a name legitimately resolves to different addresses across lookups, such as short record lifetimes or rotation between several addresses.

This issue affects safeurl: from 0.1.0 onward.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-77972?

1 open source package ship an affected version, including safeurl.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `safeurl` | Hex | From 0.1.0 | None |

## How do I fix CVE-2026-77972?

No fix has been published for CVE-2026-77972 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-77972 being exploited?

There is no known exploitation of CVE-2026-77972 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77972 and fix it if it is affected.

What it is: CVE-2026-77972 is a critical server-side request forgery vulnerability in Slab safeurl, published on 15 Sep 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-2026-77972 in the wild and no public exploit code.

Affected packages and fixed versions:
- safeurl (Hex): affected from 0.1.0; no fix listed

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-2026-77972/ (Markdown: https://insights.sbomify.com/CVE-2026-77972/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77972
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77972
- OSV: https://osv.dev/vulnerability/CVE-2026-77972

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77972/
Summaries are generated and may contain mistakes; the official description above is the record.