# CVE-2026-80255: secure cookie attribute bypass with tab

> Attackers can bypass the Secure cookie flag in curl by using tabs in headers, causing sensitive cookies to be sent over insecure HTTP connections.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A: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 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** ALPINE-CVE-2026-80255, AZL-99810, AZL-99828, AZL-99864, BELL-CVE-2026-80255, CURL-CVE-2026-80255, DEBIAN-CVE-2026-80255, ECHO-3548-ceb3-1337, GHSA-vmmm-3jqx-jgx8, MINI-pgw6-c2w6-p424, MINI-xg5x-26hr-hmrw, ROOT-OS-ALPINE-320-CVE-2026-80255, ROOT-OS-ALPINE-321-CVE-2026-80255, ROOT-OS-ALPINE-322-CVE-2026-80255, ROOT-OS-DEBIAN-13-CVE-2026-80255, UBUNTU-CVE-2026-80255

## What is CVE-2026-80255?

CVE-2026-80255 is a high-severity vulnerability in Haxx Curl, published on 6 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A `Set-Cookie:` header using tab (horizontal tab, ASCII code 9) instead of
space (ascii code 32) immediately before the `Secure` attribute causes curl to
store the cookie without its Secure flag. The cookie might then wrongfully be
sent over plaintext HTTP on subsequent requests to the same host.

Weakness: CWE-201 (Insertion of Sensitive Information Into Sent Data)

## Which versions are affected by CVE-2026-80255?

It affects 1 product.


Products: Haxx Curl.

## How do I fix CVE-2026-80255?

Upgrade to a fixed version.

## Is CVE-2026-80255 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-80255 exists.

## Other vulnerabilities in Haxx Curl

- [CVE-2026-19931](https://insights.sbomify.com/CVE-2026-19931/): Negotiate ambient user conn reuse (critical 9.8)
- [CVE-2026-10536](https://insights.sbomify.com/CVE-2026-10536/): HTTP/2 stream-dependency tree UAF (critical 9.8)
- [CVE-2026-11856](https://insights.sbomify.com/CVE-2026-11856/): cross-origin Digest auth state leak (critical 9.8)
- [CVE-2026-8925](https://insights.sbomify.com/CVE-2026-8925/): SASL double-free (critical 9.8)
- [CVE-2026-9079](https://insights.sbomify.com/CVE-2026-9079/): stale proxy password leak (critical 9.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-80255 and fix it if it is affected.

What it is: CVE-2026-80255 is a high-severity vulnerability in Haxx Curl, published on 6 Sep 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-2026-80255 exists.

Affected product: Haxx Curl. 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-2026-80255/ (Markdown: https://insights.sbomify.com/CVE-2026-80255/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-80255
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-80255
- OSV: https://osv.dev/vulnerability/CVE-2026-80255

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-80255/
Summaries are generated and may contain mistakes; the official description above is the record.