CVE-2026-28980

HIGHCVSS · not yet scored

Also known asGHSA-rj37-6j9x-74q6 (GitHub Security Advisories)

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EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • No CVSS published and no exploitation signals yet
CISA-KEV: Not listedEPSS PROB: <0.1%CVSS v2: —Exploit: None knownExposed services: Not assessed

A fixed version is listed under Patch Availability — apply it.

SwiftNIO NIOHTTP1: HTTPDecoder accepts unbounded HTTP/1 header blocks, enabling remote DoS

Summary

The HTTPDecoder in NIOHTTP1 enforces no limit on the total size of an HTTP/1 message's header block or on the number of header fields per message. A remote peer can submit an arbitrary number of small, valid headers in a single request and have them all accumulated into the resulting HTTPHeaders value before any application code runs. This can be used to exhaust memory, or — for consumers that subsequently convert headers into swift-http-types' HTTPFields — to crash the process.

Details

HTTPDecoder previously enforced only a single hardcoded parsing limit: 80 KB per individual header field (name + value). There was no cap on the cumulative size of the header block, nor on the number of header fields per message. Because each individual field can remain well below the 80 KB threshold, a peer can submit hundreds of thousands of valid headers in a single request, all of which are appended to the decoded HTTPHeaders without bound.

The headers are then visible to user code through the standard HTTPServerRequestPart.head / HTTPClientResponsePart.head events. Two observed downstream effects:

  • Hummingbird 2 (and other consumers that bridge HTTPHeaders into swift-http-types' HTTPFields) crashes via a precondition failure inside HTTPFields once the configured field count is exceeded.
  • Vapor 4 does not crash, but the per-request memory footprint scales linearly with the number of headers received, allowing a single connection to inflate server memory use substantially.

Impact

A single unauthenticated remote peer can trigger a denial of service against any HTTP/1 server (or, in the response direction, any HTTP/1 client) built on NIOHTTP1 — either by crashing the process, depending on the downstream framework, or by driving the process's resident memory to arbitrary sizes.

Patches

This issue is addressed in swift-nio 2.100.0 and later.

The HTTPDecoder now applies three parsing limits with conservative defaults, exposed through the new NIOHTTPDecoderLimitConfiguration type:

| Limit | Default | | --- | --- | | maxHeaderFieldSize | 80 KB | | maxHeaderListSize | 2 MB | | maxHeaderFieldCount | 256 |

Exceeding any of these limits causes the decoder to fail with HTTPParserError.headerOverflow. The configuration can be supplied directly to HTTPRequestDecoder / HTTPResponseDecoder, or via the decoderConfiguration property on NIOUpgradableHTTPServerPipelineConfiguration and NIOUpgradableHTTPClientPipelineConfiguration.

Users who require larger limits — for example, applications that legitimately exchange very large header blocks — can opt into them explicitly by constructing a custom NIOHTTPDecoderLimitConfiguration.

Workarounds

Users unable to upgrade can mitigate by placing a reverse proxy in front of the service that enforces equivalent limits on request header count and total header size.

Credit

This issue was reported by @Joannis. SwiftNIO thanks @Joannis for the report and the support in landing the fix.

CVSS v3
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EchelonGraph score
Not yet assessedNo source has published severity data for this CVE yet — no CVSS score from NVD or a CNA, no GitHub advisory, and it is not in CISA KEV. This is not a rating of zero; we cannot assess it yet.
EG Score
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EG Risk
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EPSS PROB
<0.1%
EPSS %ILE
15th
KEV
Not listed

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

EG Severity
Not assessed: no CVSS publishedA missing CVSS is not a severity of zero.
EG Likelihood
<0.1% within 30 daysSource: FIRST EPSS. FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
No SSVC decision: EchelonGraph has not assessed this CVECISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the BOD 26-04 block below.

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

June 12, 2026

Last Modified

June 12, 2026

Vendor Advisories for CVE-2026-28980(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(1)

Vendor / EcosystemFix (by version range) / PatchReleasedSource
swiftgithub.com/apple/swift-nio @ 2.100.0 (fixes <= 2.99.0)—ghsa

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 1× in last 7d / 7× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-11-01 07:55 UTCGHSA enrichmentGHSA-rj37-6j9x-74q6 · GitHub severity HIGH
  2. 2026-10-25 14:37 UTCEG score recompute
  3. 2026-10-18 03:50 UTCEG score recompute
  4. 2026-10-12 16:16 UTCEG score recompute
  5. 2026-10-11 19:58 UTCEG score recompute
  6. 2026-10-11 17:12 UTCEG score recompute
  7. 2026-10-11 14:41 UTCEG score recompute
  8. 2026-08-01 14:06 UTCEG score recompute
  9. 2026-07-26 20:43 UTCEG score recompute
  10. 2026-07-23 03:08 UTCEG score recompute
  11. 2026-06-14 23:18 UTCEPSS rescoreEPSS <0.1% · 15th percentile
  12. 2026-06-13 23:00 UTCEPSS rescoreEPSS <0.1% · 15th percentile
  13. 2026-06-12 15:11 UTCEG score recompute

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Frequently asked(4)

What is CVE-2026-28980?
CVE-2026-28980 is a high-severity vulnerability; its CVE record was published on June 12, 2026. SwiftNIO NIOHTTP1: HTTPDecoder accepts unbounded HTTP/1 header blocks, enabling remote DoS Summary The HTTPDecoder in NIOHTTP1 enforces no limit on the total size of an HTTP/1 message's header block or on the number of header fields per message. A remote peer can submit an arbitrary number of…
When was the CVE record for CVE-2026-28980 published?
The CVE record for CVE-2026-28980 was published on June 12, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of June 12, 2026; the record at its source may have been updated since.
Is CVE-2026-28980 actively exploited?
CVE-2026-28980 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a <0.1% probability of exploitation in the next 30 days (15th percentile of EPSS-scored CVEs).
How do I remediate CVE-2026-28980?
A fixed version for CVE-2026-28980 is listed under Patch Availability on this page: update to the version listed for your package. The vendor advisories EchelonGraph has for CVE-2026-28980 are linked in the Vendor Advisories panel on this page.

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