# CVE-2026-45352: cpp-httplib DoS: Negative chunk-size in chunked Transfer-Encoding

> A remote attacker can crash the server or exhaust memory by sending a negative chunk size in HTTP chunked transfer encoding.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 May 2026
- **Updated:** 2 Jun 2026
- **Also known as:** DEBIAN-CVE-2026-45352, GHSA-h6wq-j5mv-f3q8, UBUNTU-CVE-2026-45352

## What is CVE-2026-45352?

CVE-2026-45352 is a medium-severity denial of service vulnerability in yhirose cpp-httplib, published on 29 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.43.4, negative chunk-size in chunked Transfer-Encoding causes unbounded memory allocation and process crash. The ChunkedDecoder::read_payload function in cpp-httplib (httplib.h) parses the chunk-size field of HTTP chunked transfer encoding using std::strtoul(). Per the C standard (§7.22.1.4), strtoul silently accepts a leading minus sign, performing unsigned wrap-around: strtoul("-2", …, 16) returns ULONG_MAX − 1 (0xFFFFFFFFFFFFFFFE). The library's only guard (line 12833) rejects ULONG_MAX (the result of "-1"), but any other negative value such as "-2" passes validation. The resulting near-maximum value is stored in chunk_remaining and controls how many bytes the server's read loop consumes from the network. This vulnerability is fixed in 0.43.4.

Weakness: CWE-770 (Allocation of Resources Without Limits or Throttling), CWE-20 (Improper Input Validation), CWE-1285 (Improper Validation of Specified Index, Position, or Offset in Input)

## Which versions are affected by CVE-2026-45352?

It affects 1 product.


Products: Yhirose Cpp-Httplib.

## How do I fix CVE-2026-45352?

Upgrade to a fixed version.

## Is CVE-2026-45352 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-45352 exists.

## Other vulnerabilities in yhirose cpp-httplib

- [CVE-2025-66570](https://insights.sbomify.com/CVE-2025-66570/): cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*) (critical 10.0)
- [CVE-2026-45372](https://insights.sbomify.com/CVE-2026-45372/): cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection (critical 9.9)
- [CVE-2026-46527](https://insights.sbomify.com/CVE-2026-46527/): Null dereference in cpp-httplib (high 8.7)
- [CVE-2026-32627](https://insights.sbomify.com/CVE-2026-32627/): cpp-httplib has a Silent TLS Certificate Verification Bypass on HTTPS Redirect via Proxy (high 8.7)
- [CVE-2026-22776](https://insights.sbomify.com/CVE-2026-22776/): cpp-httplib vulnerable to a denial of service (DOS) using a zip bomb (high 8.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45352 and fix it if it is affected.

What it is: CVE-2026-45352 is a medium-severity denial of service vulnerability in yhirose cpp-httplib, published on 29 May 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-2026-45352 exists.

Affected product: yhirose cpp-httplib. 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-2026-45352/ (Markdown: https://insights.sbomify.com/CVE-2026-45352/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45352
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45352
- OSV: https://osv.dev/vulnerability/CVE-2026-45352

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-45352/
Summaries are generated and may contain mistakes; the official description above is the record.