# CVE-2026-0994: Denial of Service in Python Protobuf

> An attacker can cause a denial of service by bypassing recursion limits in Python Protobuf's JSON parser using deeply nested Any messages.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jan 2026
- **Updated:** 1 Sep 2026
- **Also known as:** ALSA-2026:3094, ALSA-2026:3095, AZL-75830, AZL-76481, AZL-76487, AZL-76505, AZL-76602, BELL-CVE-2026-0994, CLEANSTART-2026-AQ60888, CLEANSTART-2026-PH08344, CLEANSTART-2026-RQ34682, CLEANSTART-2026-WA39433, CLEANSTART-2026-WB32987, CLEANSTART-2026-WT17870, CLSA-2026-1770768843, CLSA-2026-1772451263, CLSA-2026-1772453362, CLSA-2026-1788858730, CLSA-2026-1791188851, DEBIAN-CVE-2026-0994, ECHO-1995-ff5e-ce0c, GHSA-7gcm-g887-7qv7, MINI-8c2p-3hx7-chxg, MINI-9p84-2f66-w8g6, MINI-chjg-5c76-pf73, MINI-f9mc-r9fc-g3fx, MINI-ggq5-7v34-9phx, MINI-h4v9-6r3g-p4x2, MINI-pj43-xq9f-j692, MINI-rv9c-v782-3mf2, MINI-vcvc-7f9g-7xj3, OESA-2026-1432, PYSEC-2026-1805, RHSA-2026:3059, RHSA-2026:3094, RHSA-2026:3095, RHSA-2026:3097, RHSA-2026:3218, RHSA-2026:3219, RHSA-2026:3220, RLSA-2026:3094, RLSA-2026:3095, ROOT-APP-PYPI-CVE-2026-0994, SUSE-SU-2026:0374-1, SUSE-SU-2026:0517-1, SUSE-SU-2026:0563-1, SUSE-SU-2026:0618-1, SUSE-SU-2026:20352-1, SUSE-SU-2026:20490-1, UBUNTU-CVE-2026-0994, USN-8063-2, openSUSE-SU-2026:10515-1

## What is CVE-2026-0994?

CVE-2026-0994 is a high-severity denial of service vulnerability in Python Protobuf, published on 23 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A denial-of-service (DoS) vulnerability exists in google.protobuf.json_format.ParseDict() in Python, where the max_recursion_depth limit can be bypassed when parsing nested google.protobuf.Any messages.

Due to missing recursion depth accounting inside the internal Any-handling logic, an attacker can supply deeply nested Any structures that bypass the intended recursion limit, eventually exhausting Python’s recursion stack and causing a RecursionError.

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2026-0994?

5 open source packages ship an affected version, including protobuf. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `protobuf` | PyPI | All versions | 5.29.6, 6.33.5 |
| `protobuf` | PyPI | All versions | 5.29.6 |
| `protobuf` | PyPI | All versions | 5.29.6 |
| `protobuf` | PyPI | From 6.30.0rc1 | 6.33.5 |
| `protobuf` | PyPI | From 6.30.0rc1 | 6.33.5 |
| `protobuf` | AlmaLinux:10 | All versions | 3.19.6-15.el10_1 |
| `protobuf-compiler` | AlmaLinux:10 | All versions | 3.19.6-15.el10_1 |
| `protobuf-devel` | AlmaLinux:10 | All versions | 3.19.6-15.el10_1 |
| `protobuf-lite` | AlmaLinux:10 | All versions | 3.19.6-15.el10_1 |
| `protobuf-lite-devel` | AlmaLinux:10 | All versions | 3.19.6-15.el10_1 |
| `python3-protobuf` | AlmaLinux:10 | All versions | 3.19.6-15.el10_1 |
| `protobuf` | AlmaLinux:9 | All versions | 3.14.0-17.el9_7 |
| `protobuf-compiler` | AlmaLinux:9 | All versions | 3.14.0-17.el9_7 |
| `protobuf-devel` | AlmaLinux:9 | All versions | 3.14.0-17.el9_7 |
| `protobuf-lite` | AlmaLinux:9 | All versions | 3.14.0-17.el9_7 |
| `protobuf-lite-devel` | AlmaLinux:9 | All versions | 3.14.0-17.el9_7 |
| `python3-protobuf` | AlmaLinux:9 | All versions | 3.14.0-17.el9_7 |
| `protobuf` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-compiler` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-compiler-debuginfo` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-debuginfo` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-debugsource` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-devel` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-lite` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-lite-debuginfo` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf-lite-devel` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `python3-protobuf` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `python3-protobuf-debuginfo` | Red Hat:enterprise_linux:10.1 | All versions | 0:3.19.6-15.el10_1 |
| `protobuf` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-compiler-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-debugsource` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-lite` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-lite-debuginfo` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `python3-protobuf` | Red Hat:enterprise_linux:9::appstream | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-compiler` | Red Hat:enterprise_linux:9::crb | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-compiler-debuginfo` | Red Hat:enterprise_linux:9::crb | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-debuginfo` | Red Hat:enterprise_linux:9::crb | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-debugsource` | Red Hat:enterprise_linux:9::crb | All versions | 0:3.14.0-17.el9_7 |
| `protobuf-devel` | Red Hat:enterprise_linux:9::crb | All versions | 0:3.14.0-17.el9_7 |

Products: Google Protobuf.

## How do I fix CVE-2026-0994?

Upgrade protobuf to a fixed version for your release line: 5.29.6 or 6.33.5.

## Is CVE-2026-0994 being exploited?

There is no known exploitation of CVE-2026-0994 in the wild and no public exploit code.

Public exploit code:

- Ruby/PHP upb Any-recursion audit: falsified vs CVE-2026-0994 bug class (github_poc): https://github.com/Vardhan0257/upb-any-recursion-audit

## Other vulnerabilities in Python Protobuf

- [CVE-2015-5237](https://insights.sbomify.com/CVE-2015-5237/): Memory corruption in n/a (high 8.8)
- [CVE-2024-7254](https://insights.sbomify.com/CVE-2024-7254/): Stack overflow in Protocol Buffers Java Lite (high 8.7)
- [CVE-2024-2410](https://insights.sbomify.com/CVE-2024-2410/): Use after free in C++ protobuf (high 7.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-0994 and fix it if it is affected.

What it is: CVE-2026-0994 is a high-severity denial of service vulnerability in Python Protobuf, published on 23 Jan 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-2026-0994 in the wild and no public exploit code.

Affected packages and fixed versions:
- protobuf (PyPI): affected all versions; fixed in 5.29.6, 6.33.5
- protobuf (PyPI): affected all versions; fixed in 5.29.6
- protobuf (PyPI): affected all versions; fixed in 5.29.6
- protobuf (PyPI): affected from 6.30.0rc1; fixed in 6.33.5
- protobuf (PyPI): affected from 6.30.0rc1; fixed in 6.33.5

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-2026-0994/ (Markdown: https://insights.sbomify.com/CVE-2026-0994/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-0994
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-0994
- OSV: https://osv.dev/vulnerability/CVE-2026-0994

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-0994/
Summaries are generated and may contain mistakes; the official description above is the record.