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🛡️ CVE-2026-7790 — cowlib

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-400 OSV
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS

Summary

Uncontrolled Resource Consumption vulnerability in ninenines cowlib (cow\_http\_te module) allows Excessive Allocation.

The chunked transfer-encoding parser in cow\_http\_te accepts an unbounded number of hex digits in the chunk-size field. Each digit causes a bignum multiplication (Len \* 16 + digit), so parsing N hex digits requires O(N²) CPU work and O(N) memory. Additionally, when input is drip-fed, the parser discards the accumulated length on each partial read and restarts from zero on resumption, raising the cost to O(N³). An unauthenticated remote attacker can exploit this by sending an HTTP/1.1 request with Transfer-Encoding: chunked and a very long chunk-size hex string to cause denial of service through CPU exhaustion and memory amplification.

This vulnerability is associated with program file src/cow\_http\_te.erl and program routines cow\_http\_te:stream\_chunked/2, cow\_http\_te:chunked\_len/4.

This issue affects cowlib: from 0.6.0 before 2.16.1.

Workaround

In Cowboy, setting initial\_stream\_flow\_size to a much lower value limits the amount of chunked body data that cowlib will parse in a single read, reducing the window of data an attacker can use to trigger the quadratic work. This does not fully eliminate the vulnerability but can significantly reduce its impact for some applications.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: 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

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Attack requirements: None — no deployment-specific condition has to hold.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-7790 is classified as CWE-400: Uncontrolled Resource Consumption. A request can consume memory, CPU or storage without limit, exhausting capacity for everyone else.

Affected software

CVE-2026-7790 is recorded against 1 package.

  • cowlib

Timeline and source

Published on 11 May 2026 and last revised on 30 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

cna.erlef.org (Web)
github.com (Fix)
hex.pm (Package)

Other advisories for this package

cowlib has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-400: Uncontrolled Resource Consumption) in other software:

CVE-2026-7790 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector 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
CWE CWE-400
Public Exploit ✅ No
Source OSV
Published 2026-05-11
Updated 2026-08-20
Modified 2026-07-30

Affected Packages

Software From version Fixed in
cowlib — —

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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