# CVE-2026-31838: Auth bypass in istio

> Attackers can bypass Istio authorization policies by crafting requests with multiple HTTP header values, allowing unauthorized access to protected services.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:L/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 10 Mar 2026
- **Updated:** 7 Apr 2026
- **Also known as:** CLEANSTART-2026-WL80869, GHSA-974c-2wxh-g4ww, MINI-24q2-57pm-6v2h, MINI-37wr-554w-896r, MINI-5289-c532-2c86, MINI-5549-qf3g-q56g, MINI-57m3-f3vr-mq99, MINI-5p5w-gf8m-xch3, MINI-5pqx-mhf5-4h46, MINI-7g5f-p6mj-j2c8, MINI-948f-83w5-pwq5, MINI-gpwc-mfq2-8vrh, MINI-hj96-7854-q459, MINI-pjw8-pfrj-pvf7, MINI-pxh5-4j77-x62j, MINI-r3p3-63gh-g9wm, MINI-vpmv-r483-527c, MINI-xjr3-c539-xfvv

## What is CVE-2026-31838?

CVE-2026-31838 is a medium-severity authentication bypass vulnerability in istio, published on 10 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Istio is an open platform to connect, manage, and secure microservices. Prior to 1.29.1, 1.28.5, and 1.27.8, a vulnerability in Envoy RBAC header matching could allow authorization policy bypass when policies rely on HTTP headers that may contain multiple values. An attacker could craft requests with multiple header values in a way that causes Envoy to evaluate the header differently than intended, potentially bypassing authorization checks. This may allow unauthorized requests to reach protected services when policies depend on such header-based matching conditions. This vulnerability is fixed in 1.29.1, 1.28.5, and 1.27.8.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-31838?

It affects 1 product.


Products: Istio Istio.

## How do I fix CVE-2026-31838?

Upgrade to a fixed version.

## Is CVE-2026-31838 being exploited?

There is no known exploitation of CVE-2026-31838 in the wild and no public exploit code.

## Other vulnerabilities in istio

- [CVE-2021-31921](https://insights.sbomify.com/CVE-2021-31921/): Missing authorization in n/a (critical 9.8)
- [CVE-2021-34824](https://insights.sbomify.com/CVE-2021-34824/): Information disclosure in n/a (high 8.8)
- [CVE-2026-31837](https://insights.sbomify.com/CVE-2026-31837/): Istio JWKS resolver to prevent private key material from being exposed when JWKS fetch fails. (high 8.7)
- [CVE-2021-39155](https://insights.sbomify.com/CVE-2021-39155/): Authorization Policy Bypass Due to Case Insensitive Host Comparison (high 8.3)
- [CVE-2021-39156](https://insights.sbomify.com/CVE-2021-39156/): Fragments in Path May Lead to Authorization Policy Bypass (high 8.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-31838 and fix it if it is affected.

What it is: CVE-2026-31838 is a medium-severity authentication bypass vulnerability in istio, published on 10 Mar 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-2026-31838 in the wild and no public exploit code.

Affected product: istio. 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-2026-31838/ (Markdown: https://insights.sbomify.com/CVE-2026-31838/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-31838
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-31838
- OSV: https://osv.dev/vulnerability/CVE-2026-31838

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-31838/
Summaries are generated and may contain mistakes; the official description above is the record.