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.
No advisories yet.
Solution
No solution given by the vendor.
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.
Mon, 11 May 2026 19:15:00 +0000
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| Metrics |
ssvc
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Mon, 11 May 2026 18:45:00 +0000
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| Description | 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. | |
| Title | Unbounded chunk-size hex digits in cowlib cause quadratic CPU and memory DoS | |
| First Time appeared |
Ninenines
Ninenines cowlib |
|
| Weaknesses | CWE-400 | |
| CPEs | cpe:2.3:a:ninenines:cowlib:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Ninenines
Ninenines cowlib |
|
| References |
| |
| Metrics |
cvssV4_0
|
Projects
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Status: PUBLISHED
Assigner: EEF
Published:
Updated: 2026-05-11T18:56:31.426Z
Reserved: 2026-05-04T18:23:21.380Z
Link: CVE-2026-7790
Updated: 2026-05-11T18:56:27.213Z
Status : Received
Published: 2026-05-11T19:16:29.477
Modified: 2026-05-11T19:16:29.477
Link: CVE-2026-7790
No data.
OpenCVE Enrichment
Updated: 2026-05-11T19:30:06Z