Vulnerability in cowlib (CVE-2026-7790)
Summary
Vulnerability in cowlib (CVE-2026-7790). Risk of unauthorized operations or information disclosure. Mitigation: upgrade to 2.16.1 or later.
Original description
The description as published by the source.
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.
Workarounds
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-7790 has been found in cowlib.
Risk of unauthorized operations or information disclosure.
What to do: upgrade cowlib to 2.16.1 or later.
If unsure, ask your IT team or search "cowlib CVE-2026-7790" on the vendor's site.
CVE-2026-7790 (cowlib) — CWE-400
Patched: 2.16.1 — apply immediately
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.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-400) exists in cowlib.
Check the vendor advisory for the affected versions of cowlib.
Severity: ?. Risk of unauthorized operations or information disclosure.
Update to 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.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'cowlib' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'cowlib' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
cowlibを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
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.パッチが適用されるまでの応急処置として、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. を実施。回避策の副作用 (機能低下) を確認した上で。
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3Apply patch patch
Upgrade cowlib to 2.16.1ステージング環境で 2.16.1 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
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4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-7790 erlang-cowlib
- Ubuntu UBUNTU-CVE-2026-7790 erlang-cowlib
References
- advisory nvd.nist.gov
- package github.com
- package hex.pm
- patch github.com
- web cna.erlef.org
- web osv.dev
- web github.com
- web github.com