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Response snapshot Oct 27, 2026, 07:53 UTC

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VulnerabilityCVE-2026-115776

Twisted: Unauthenticated Remote Denial of Service in the Twisted IRC Server via an Unbounded Line Buffer

An unbounded-buffer vulnerability (CWE-770) in the Twisted words IRC server lets any unauthenticated remote client exhaust server memory. `twisted.words.protocols.irc.IRC.

At a glance

Exploited
Not known
Severity
7.5 High (CVSS 3.1)
Chance of exploitation
0.5% in the next 30 days
Sources
2 independent sources

What to do

GitHub lists first patched versions: Twisted: 26.10.0rc1. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-53xc-49m8-p798 (opens a new tab)

What happened

## Summary

An unbounded-buffer vulnerability (CWE-770) in the Twisted words IRC server lets any unauthenticated remote client exhaust server memory. `twisted.words.protocols.irc.IRC.dataReceived` appends every received byte to a per-connection buffer and only removes data at a line feed, with no maximum length.

Because `IRC` is a plain `Protocol` and not a `LineReceiver`, one connection that streams bytes without a line feed grows the buffer without bound and drives the whole single-threaded process to out-of-memory, dropping every user at once. The `twistd words` server inherits the method unchanged through `IRCUser`, and the data is buffered before any authentication.

## Details

Continue reading

`IRC.dataReceived` keeps everything up to the last line feed in `self.buffer`:

```python # twisted/words/protocols/irc.py class IRC(protocol.Protocol): # not a LineReceiver, so no MAX_LENGTH buffer = "" def dataReceived(self, data): if isinstance(data, bytes): data = data.decode("utf-8") lines = (self.buffer + data).split(LF) self.buffer = lines.pop() # no 3line feed -> whole input stays buffered ... ```

With no line feed in the data, `lines.pop()` returns the entire accumulated content to `self.buffer`, so it grows by every chunk and is never bounded; `IRC` defines no `MAX_LENGTH`, no `lineLengthExceeded`, and no timeout, so the connection is never closed. The `twistd words` server protocol `IRCUser` subclasses `IRC` without overriding `dataReceived`, and the buffer is filled before any `PASS`, `NICK`, or `USER`, so no credentials are required.

Affected product: Twisted (`twisted.words`), `twisted.words.protocols.irc.IRC` and its subclass `twisted.words.service.IRCUser` Affected versions: 26.4.0 and earlier

## PoC

On a standard Twisted words IRC server (the server `twistd words` runs, using `IRCUser`), an unauthenticated client opens a single TCP connection and continuously sends data that contains no line feed, never completing a line. Every chunk is appended to the connection's line buffer, and because no complete line is ever formed none of it is consumed, so the buffer grows by the full volume sent.

In a measured run against a real `IRCFactory` server, one unauthenticated connection sending 60 MB of line-feed-free data raised the server process resident memory from about 47 MB to 2966 MB (roughly 49 MB per MB sent) with the connection still open and no limit triggered. Sending the same volume as normal line-feed-terminated commands leaves memory flat, which isolates the cause to the missing line-length bound.

## Impact

An unauthenticated remote denial of service from allocation without limits (CWE-770) leading to uncontrolled resource consumption (CWE-400). A single credential-free connection exhausts the memory of the whole `twistd words` process, and because one process serves every user, the crash drops all connections at once and the service stays down until it is restarted.

The quadratic buffer copy reaches the same effect faster. There is no confidentiality or integrity impact and no code execution.

Affected package ranges reported by GitHub: Twisted: <= 26.4.0

Scores and how they were measured

CVSS base severity

7.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Measurement source (opens a new tab)

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

EPSS probability

0.5%

Scored Percentile 42.6%

Model and measurement source (opens a new tab)

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

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-53xc-49m8-p798 (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-53xc-49m8-p798, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-53xc-49m8-p798, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  4. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-53xc-49m8-p798, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  5. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-53xc-49m8-p798, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  6. Primary source

    NVD CVE-2026-115776 (opens a new tab)

    NVD record: description, CVSS (the CNA score is preferred), affected products, and publication date. Not evidence of exploitation.

    Published Checked

  7. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  8. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  9. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  10. Primary source

    NVD CVE API 2.0 (opens a new tab)

    The NVD API page that supplied this CVE record.

    Published Date not suppliedChecked

  11. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-115776, scored 2026-10-26. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

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

APA

KEVWire. (2026, October 26). Twisted: Unauthenticated Remote Denial of Service in the Twisted IRC Server via an Unbounded Line Buffer (CVE-2026-115776). https://kevwire.com/record/CVE-2026-115776

MLA

"Twisted: Unauthenticated Remote Denial of Service in the Twisted IRC Server via an Unbounded Line Buffer (CVE-2026-115776)." KEVWire, 26 Oct. 2026, kevwire.com/record/CVE-2026-115776.

Chicago

KEVWire. "Twisted: Unauthenticated Remote Denial of Service in the Twisted IRC Server via an Unbounded Line Buffer (CVE-2026-115776)." Last modified October 26, 2026. https://kevwire.com/record/CVE-2026-115776.

Evidence summary (plain text)

Twisted: Unauthenticated Remote Denial of Service in the Twisted IRC Server via an Unbounded Line Buffer (Oct 23, 2026).
An unbounded-buffer vulnerability (CWE-770) in the Twisted words IRC server lets any unauthenticated remote client exhaust server memory. `twisted.words.protocols.irc.IRC.dataReceived` appends every received byte to a per-connection buffer and only removes data at a line feed, with no maximum length. Because `IRC` is a plain `Protocol` and not a `LineReceiver`, one connection that streams bytes without a line feed grows the buffer without bound and drives the whole single-threaded process to out-of-memory, dropping every user at once. The `twistd words` server inherits the method unchanged through `IRCUser`, and the data is buffered before any authentication.

`IRC.dataReceived` keeps everything up to the last line feed in `self.buffer`:
CVSS 7.5 (version 3.1; evidence as of Oct 26, 2026; https://nvd.nist.gov/vuln/detail/CVE-2026-115776).
EPSS 0.5% for the following 30 days, scored Oct 26, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-115776&date=2026-10-26).
Sources:
GitHub-reviewed advisory GHSA-53xc-49m8-p798: https://github.com/advisories/GHSA-53xc-49m8-p798
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo1MTozMFrOAAf0Mg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0OToxMlrOAAf0LQ%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc&after=Y3Vyc29yOnYyOpK0MjAyNi0xMC0yM1QyMDo0NzoxN1rOAAf0Kg%3D%3D
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
NVD CVE-2026-115776: https://nvd.nist.gov/vuln/detail/CVE-2026-115776
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T13:46:51.330Z&lastModEndDate=2026-10-26T15:20:55.429Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T13:11:54.490Z&lastModEndDate=2026-10-26T14:45:57.368Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?lastModStartDate=2026-10-26T12:40:01.998Z&lastModEndDate=2026-10-26T14:10:55.205Z&resultsPerPage=500&startIndex=500
NVD CVE API 2.0: https://services.nvd.nist.gov/rest/json/cves/2.0?pubStartDate=2026-10-12T13:35:55.142Z&pubEndDate=2026-10-26T13:35:55.142Z&resultsPerPage=500&startIndex=9000
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-115776&date=2026-10-26
Record ID: CVE-2026-115776.
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 27, 2026, 07:41 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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