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Response snapshot Oct 31, 2026, 01:26 UTC

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VulnerabilityCVE-2026-116775

pageant: unbounded frame buffering on peer-controlled 4-byte length prefix (memory-exhaustion DoS)

pageant::PageantStream reads a 4-byte big-endian length prefix from its input stream and buffers until len + 4 bytes are available, without ever validating len.

Published Updated

At a glance

Exploited
Not known
Severity
2.3 Low (CVSS 4.0)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: pageant: 0.2.5. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-662x-8wvj-2276 (opens a new tab)

What happened

Summary

pageant::PageantStream reads a 4-byte big-endian length prefix from its input stream and buffers until len + 4 bytes are available, without ever validating len.

The underlying WM_COPYDATA transport physically cannot carry frames larger than 8 KiB (_AGENT_MAX_MSGLEN, the fixed-size shared memory mapping), so an oversized frame is destined to fail — but only after the re-framing task has already buffered the full claimed size.

A peer controlling the stream bytes can claim a frame of up to ~4 GiB and either stream that much data (forcing a corresponding allocation) or simply stop mid-frame and keep the partial buffer resident indefinitely.

Continue reading

Vulnerable code

pageant/src/wmmessage.rs, PageantStream::new() (the spawned re-framing task), current main:

let mut buf = BytesMut::new();
while let Ok(n) = two.read_buf(&mut buf).await {
 if n == 0 { break; }
 if buf.len() Result > {
 let mut stream = pageant::PageantStream::new().await?;
 // Claim a ~4 GiB frame, stream 256 MiB, then stall: the task buffers all of it.
 stream.write_all(&0xFFFF_F000u32.to_be_bytes()).await?;
 let chunk = vec![0u8; 256 * 1024];
 for _ in 0..1024 { stream.write_all(&chunk).await?; } // 256 MiB, frame never completed
 tokio::time::sleep(std::time::Duration::from_secs(30)).await;
 Ok(())
}

Observed on Windows 11, pageant 0.2.4 (source v0.64.1, Rust 1.99): process working set grows from ~7.4 MB to ~264.7 MB after 256 MiB is streamed, and stays there while the peer stalls; no error is ever raised. Memory grows linearly with bytes sent, up to the claimed length. (Allocation behavior additionally verified with a counting global allocator.)

Suggested fix

Reject frames that cannot fit the transport before buffering:

 let len = BigEndian::read_u32(&buf) as usize;
+ // The WM_COPYDATA transport is backed by a fixed-size shared
+ // memory mapping: larger requests can never fit. Reject them
+ // before buffering. Without this cap a malicious peer could
+ // force up to ~4 GiB of buffering by claiming a huge frame
+ // and never completing it.
+ if len.saturating_add(4) > _AGENT_MAX_MSGLEN {
+ debug!("dropping oversized Pageant request: {len} bytes");
+ break;
+ }
 if buf.len() < len + 4 {
 continue;
 }

saturating_add also removes a theoretical 32-bit len + 4 overflow. break shuts down the re-framing task (the writer observes the stream close); returning an error through the stream would work equally well. Happy to submit a PR with this change, or with any alternative you prefer.

Reporter

Tshellauth

Affected package ranges reported by GitHub: pageant: >= 0.2.0, <= 0.2.4

Scores and how they were measured

CVSS base severity

2.3

Version 4.0As of

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

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Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-662x-8wvj-2276 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-662x-8wvj-2276, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 30). pageant: unbounded frame buffering on peer-controlled 4-byte length prefix (memory-exhaustion DoS) (CVE-2026-116775). https://kevwire.com/record/CVE-2026-116775

MLA

"pageant: unbounded frame buffering on peer-controlled 4-byte length prefix (memory-exhaustion DoS) (CVE-2026-116775)." KEVWire, 30 Oct. 2026, kevwire.com/record/CVE-2026-116775.

Chicago

KEVWire. "pageant: unbounded frame buffering on peer-controlled 4-byte length prefix (memory-exhaustion DoS) (CVE-2026-116775)." Last modified October 30, 2026. https://kevwire.com/record/CVE-2026-116775.

Evidence summary (plain text)

pageant: unbounded frame buffering on peer-controlled 4-byte length prefix (memory-exhaustion DoS) (Oct 30, 2026).
pageant::PageantStream reads a 4-byte big-endian length prefix from its input stream and buffers until len + 4 bytes are available, without ever validating len. The underlying WM_COPYDATA transport physically cannot carry frames larger than 8 KiB (_AGENT_MAX_MSGLEN, the fixed-size shared memory mapping), so an oversized frame is destined to fail — but only after the re-framing task has already buffered the full claimed size.
CVSS 2.3 (version 4.0; evidence as of Oct 30, 2026; https://github.com/advisories/GHSA-662x-8wvj-2276).
Sources:
GitHub-reviewed advisory GHSA-662x-8wvj-2276: https://github.com/advisories/GHSA-662x-8wvj-2276
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-116775.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 31, 2026, 00:50 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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