CVE-2026-43970: cowlib Decompression Bomb Vulnerability

HIGH
Advisory Identifier: GHSA-84f2-rp86-235p
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CWE-409
Published
Advisory Summary

CVE-2026-43970 is a HIGH decompression bomb vulnerability (CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)) affecting cowlib libraries in the Hex ecosystem. The issue involves decompression bomb in cow_spdy:inflate/2 allows memory exhaustion via crafted spdy frame. Remediation is available by upgrading affected packages to version 2.16.1.

CVE-2026-43970 at a Glance

CVE Identifier CVE-2026-43970
GHSA Identifier GHSA-84f2-rp86-235p
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)
Affected Product cowlib
Package Ecosystem Hex
Published Date
Last Updated

How to Fix CVE-2026-43970

To remediate this vulnerability, upgrade all affected cowlib dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

cowlib fixed: 2.16.1 
Upgrade cowlib to 2.16.1
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for cowlib

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-43970, inspect your project dependencies for cowlib:

inspect dependencies for cowlib

Analyze the terminal output to locate any version of cowlib in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.16.1), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification), where the product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output. In cowlib, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in ninenines cowlib allows unauthenticated remote denial of service via memory exhaustion. cow_spdy:inflate/2 in cowlib passes peer-supplied compressed bytes directly to zlib:inflate/2 with no output size bound. The SPDY header compression dictionary (?ZDICT) is public, and zlib compresses long runs of repeated bytes at roughly 1024:1, so a few kilobytes of SPDY frame payload can decompress to gigabytes on the BEAM heap, OOM-killing the node. A single unauthenticated SPDY frame is sufficient to trigger the condition. The parsers for syn_stream, syn_reply, and headers frame types are all affected via cow_spdy:parse_headers/2. This issue affects cowlib from 0.1.0 before 2.16.1.

CVE-2026-43970 Affected cowlib Versions

1 component(s)
Fixed Versions:
2.16.1
Product / Package Ecosystem Affected Versions Fixed Version
cowlib
 Hex
≥ 0.1.0
< 2.16.1
2.16.1

References

NVD — CVE-2026-43970 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-43970
Security Fix Commit FIX COMMIT
https://github.com/ninenines/cowlib/commit/16aad3fb9f81f5cda4d1706ff0c54237c619c282
cna.erlef.org/cves/cve-2026-43970... WEB
https://cna.erlef.org/cves/CVE-2026-43970.html
cowlib Source Repository REPOSITORY
https://github.com/ninenines/cowlib
osv.dev/vulnerability/eef-c... WEB
https://osv.dev/vulnerability/EEF-CVE-2026-43970

Frequently Asked Questions

What is CVE-2026-43970?
CVE-2026-43970 is a security vulnerability in cowlib involving Decompression Bomb in cow_spdy:inflate/2 Allows Memory Exhaustion via Crafted SPDY Frame under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification).
Which cowlib versions are affected?
Affected versions include releases prior to 2.16.1 across affected packages: cowlib.
What version fixes CVE-2026-43970?
Upgrading to 2.16.1 (or the latest patched release for your respective branch) resolves the vulnerability.
Is cowlib affected?
Yes, cowlib is affected in releases prior to 2.16.1. Upgrade your dependency to 2.16.1 or later.
What CWE is associated with CVE-2026-43970?
CVE-2026-43970 is classified under CWE-409: Improper Handling of Highly Compressed Data (Data Amplification) (The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output.).
How can I check Hex dependencies for CVE-2026-43970?
Run the dependency tree command: 'inspect dependencies for cowlib'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-84f2-rp86-235p",
  "modified" : "2026-05-19T20:12:01Z",
  "published" : "2026-05-13T21:32:06Z",
  "aliases" : [ "CVE-2026-43970" ],
  "summary" : "cowlib: Decompression Bomb in cow_spdy:inflate/2 Allows Memory Exhaustion via Crafted SPDY Frame",
  "details" : "Improper Handling of Highly Compressed Data (Data Amplification) vulnerability in ninenines cowlib allows unauthenticated remote denial of service via memory exhaustion.\n\ncow_spdy:inflate/2 in cowlib passes peer-supplied compressed bytes directly to zlib:inflate/2 with no output size bound. The SPDY header compression dictionary (?ZDICT) is public, and zlib compresses long runs of repeated bytes at roughly 1024:1, so a few kilobytes of SPDY frame payload can decompress to gigabytes on the BEAM heap, OOM-killing the node. A single unauthenticated SPDY frame is sufficient to trigger the condition. The parsers for syn_stream, syn_reply, and headers frame types are all affected via cow_spdy:parse_headers/2.\n\nThis issue affects cowlib from 0.1.0 before 2.16.1.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Hex",
      "name" : "cowlib"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0.1.0"
      }, {
        "fixed" : "2.16.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-43970"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/ninenines/cowlib/commit/16aad3fb9f81f5cda4d1706ff0c54237c619c282"
  }, {
    "type" : "WEB",
    "url" : "https://cna.erlef.org/cves/CVE-2026-43970.html"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/ninenines/cowlib"
  }, {
    "type" : "WEB",
    "url" : "https://osv.dev/vulnerability/EEF-CVE-2026-43970"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-409" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-19T20:12:01Z",
    "nvd_published_at" : "2026-05-13T19:17:25Z"
  }
}