# CVE-2026-58226: Unauthenticated denial-of-service via unbounded HPACK integer decoding in hpax

> Unauthenticated attackers can cause denial of service in Elixir applications using the hpax library by sending crafted HTTP/2 headers that trigger excessive CPU usage.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/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:** 6 Jul 2026
- **Updated:** 6 Jul 2026
- **Also known as:** EEF-CVE-2026-58226, GHSA-jj2p-32j7-whj2

## What is CVE-2026-58226?

CVE-2026-58226 is a high-severity denial of service vulnerability in elixir-mint hpax, published on 6 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Inefficient Algorithmic Complexity vulnerability in elixir-mint hpax allows unauthenticated denial-of-service via unbounded HPACK integer decoding.

hpax decodes HPACK variable-length integers with no upper bound on the decoded value or the number of continuation octets. 'Elixir.HPAX.Types':decode_remaining_integer/3 accumulates the integer as int + (value <<< m), shifting by 7 more bits for each continuation octet and stopping only on a terminating octet or truncated input, never because the integer grew too large. Because BEAM integers are arbitrary precision, a run of N continuation octets builds an O(N)-bit bignum and re-adds into an ever-larger bignum on each step, so the total decoding cost is superlinear (about O(N^2)). An unauthenticated attacker who can send an HTTP/2 header block to a server using this decoder (reached through the 'Elixir.HPAX':decode/2 entry point) can supply a small header block that forces a large, attacker-controlled amount of CPU (and transient memory), a denial-of-service amplification.

This issue affects hpax from 0.1.1 before 1.0.4.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-58226?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `hpax` | Hex | From 0.1.1 | 1.0.4 |

## How do I fix CVE-2026-58226?

Upgrade hpax to 1.0.4 or later.

## Is CVE-2026-58226 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-58226 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-58226 and fix it if it is affected.

What it is: CVE-2026-58226 is a high-severity denial of service vulnerability in elixir-mint hpax, published on 6 Jul 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-2026-58226 exists.

Affected packages and fixed versions:
- hpax (Hex): affected from 0.1.1; fixed in 1.0.4

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-2026-58226/ (Markdown: https://insights.sbomify.com/CVE-2026-58226/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-58226
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-58226
- OSV: https://osv.dev/vulnerability/CVE-2026-58226

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-58226/
Summaries are generated and may contain mistakes; the official description above is the record.