CVE
gRPC Server denial of service via HTTP/2 flow-control leak
- Exploited
- No known exploitation
- Fix
- Fixed in 1.1.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 1.1.0.
- Published
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 33/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
The elixir-grpc grpc_server software mishandles calls that it refuses early on HTTP/2 connections. A remote attacker, without logging in, can send such calls so that their data is still in flight, which uses up the connection's flow-control window and stalls all later calls on that shared connection until they time out.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original description
Missing Release of Resource after Effective Lifetime vulnerability in elixir-grpc grpc_server allows a client to stall all later calls on a shared HTTP/2 connection via calls that the server refuses while their DATA frames are in flight.
The stream handler grpc_stream_h (grpc_server/src/grpc_stream_h.erl) requests flow from Cowboy only for request data that has arrived. When the server refuses a call early, for example because the body exceeds max_body_size or the method is not implemented, Cowboy drops the DATA frames still in flight for that stream. Their bytes are not returned to the connection flow-control window. After enough refused calls the window is empty. No call on that connection can then send a request body, and each call waits until its deadline. Other connections are not affected.
This issue affects grpc_server: from 1.0.0 before 1.1.0.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed per the CVSS vector, reachable over the network without a login · Unknown: No advisory context yet
- Reach10/20Affects Hex packages
- Severity6.3/10CVSS 6.3
- No patch0/5No signal
What would change the score
- Would score about 78 if added to CISA KEV
- Would score about 73 if CISA's SSVC rates exploitation active
- Would score about 38 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 1.1.0.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-123635 (Refused calls drain the HTTP/2 connection flow-control window in elixir-grpc grpc_server), using the cve.now data below.
Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only.
What cve.now has for CVE-2026-123635 (entry last updated 2026-11-13):
Affected:
- Hex package grpc_server: from 1.0.0, fixed in 1.1.0
- elixir-grpc grpc_server: version range not reported
- Hex package grpc_server: from 1.0.0, fixed in 1.1.0
Fixed versions: 1.1.0.
Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory.
CISA KEV: CVE-2026-123635 is not listed as of cve.now's last read.
This KEV status is for CVE-2026-123635 only. If you also check another CVE, look up its own KEV status; never assume it from this one.
How to check:
- Packages (Hex): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies.
Verify against the linked advisories before concluding, and cite the date you read each one:
- https://github.com/elixir-grpc/grpc/security/advisories/GHSA-7x9q-vvph-rjcr
- https://github.com/elixir-grpc/grpc/commit/61a71948e6e7b95efb27d48e7084c764503cc802
- https://cna.erlef.org/cves/CVE-2026-123635.html
- https://osv.dev/vulnerability/EEF-CVE-2026-123635
- https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing.
Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action.
Entry: https://cve.now/CVE-2026-123635
For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "CVE-2026-123635"}.Timeline
- CVE published
- First seen by cve.now
Affected versions
- grpc_serverHex
From 1.0.0 · fixed in 1.1.0
- elixir-grpc/grpc
Version range not reported
- grpc_serverHex
From 1.0.0 · fixed in 1.1.0
Evidence 7
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-123635
Is CVE-2026-123635 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-123635?
grpc_server (Hex): from 1.0.0 before 1.1.0. grpc_server (Hex): from 1.0.0 before 1.1.0.Source: cve.now feed data
How do I fix CVE-2026-123635?
Upgrade to a fixed version: 1.1.0.Source: cve.now feed data