CVE-2026-43970

CVE-2026-43970 is a high-severity vulnerability with a CVSS 4.0 base score of 8.2. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-409.

Key facts

Description

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.

Frequently asked questions

What is CVE-2026-43970?
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.
How severe is CVE-2026-43970?
CVE-2026-43970 has a CVSS 4.0 base score of 8.2, rated high severity.
Is CVE-2026-43970 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (40th percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-43970?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-43970 have an EU (EUVD) identifier?
Yes. CVE-2026-43970 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-30131.
When was CVE-2026-43970 published?
CVE-2026-43970 was published on 2026-05-13 and last updated on 2026-06-17.

References

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