# CVE-2026-45100: OpenSIPS: Buffer Overflow in Base64 Encode Transformation

> A remote attacker can trigger a buffer overflow in OpenSIPS via large SIP headers if the routing script uses base64 encoding, potentially leading to code execution or crashes.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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:** No
- **Published:** 4 Aug 2026
- **Updated:** 5 Aug 2026
- **Also known as:** GHSA-35fr-6rv9-vp68, UBUNTU-CVE-2026-45100

## What is CVE-2026-45100?

CVE-2026-45100 is a critical memory corruption vulnerability in opensips, published on 4 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

OpenSIPS is a Session Initiation Protocol (SIP) server implementation. Versions 3.4.0-beta through 3.6.5 and 4.0.0-beta contain a buffer overflow in the {s.b64encode} string transformation. The size check for {s.b64encode} only verifies that the input fits within the 64 KB transformation buffer, but base64 encoding expands the data by roughly a third, so an input between about 49,153 and 65,535 bytes produces more output than the buffer can hold and overflows it by up to 21,844 bytes. Because these transformation buffers sit next to each other in memory and are reused for chained transformations, the overflow writes attacker-controlled data into the adjacent buffer and corrupts values used by later transformations processing the same SIP message. A remote attacker can trigger this by sending a SIP message with a large header value (roughly 50,000 bytes or more) when the routing script applies  {s.b64encode}  to attacker-controlled input, making exploitability dependent on the deployment's routing configuration. This issue has been fixed in versions 3.6.6 and 4.0.0-rc1.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2026-45100?


## How do I fix CVE-2026-45100?

No fix has been published for CVE-2026-45100 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-45100 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45100 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45100 and fix it if it is affected.

What it is: CVE-2026-45100 is a critical memory corruption vulnerability in opensips, published on 4 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45100 exists.

Affected product: opensips. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-45100/ (Markdown: https://insights.sbomify.com/CVE-2026-45100/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45100
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45100
- OSV: https://osv.dev/vulnerability/CVE-2026-45100

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45100/
Summaries are generated and may contain mistakes; the official description above is the record.