Gdb: gdbserver: heap disclosure and wild pointer in gdb_parse_agent_expr via untrusted agent-expression length
Affects gdbserver as shipped with Red Hat Enterprise Linux 6 through 10 and Red Hat Hardened Images, when its port is reachable over the network. No fix is listed yet.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- No fix listed
- Who is exposed
- Not reported
Do first: Workaround: Until a fix is available, keep gdbserver ports off the network, for example by binding it to localhost or blocking the port with a firewall. Stop gdbserver when it is not needed.
- Published
- Last modified
- 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? →
- 43/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- 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
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
Gdbserver, the remote debugging component of GDB, is affected. A remote attacker who does not need to log in can send a crafted agent expression to it, which lets them read uninitialized heap memory (including addresses that could help defeat ASLR) and crash the process, causing a denial of service.
Read the original description
A length validation flaw in gdbserver's agent-expression parser allows an unauthenticated remote attacker to read uninitialized heap memory from the gdbserver process and cause a denial of service. Disclosed heap content includes addresses suitable for defeating ASLR in further exploitation.
cve.now Index
- Exploitation0/40No signal
- Exposure20/25No login or user action needed, CISA rates it automatable · Unknown: Advisories don't say whether default setups are affected
- Reach10/20Shipped in major Linux distributions
- Severity8.2/10CVSS 8.2
- No patch5/5No patch listed yet
What would change the score
- Would score about 88 if added to CISA KEV
- Would score about 83 if CISA's SSVC rates exploitation active
- Would score about 48 if advisories confirm default setups are exposed
What to do
Workaround: Until a fix is available, keep gdbserver ports off the network, for example by binding it to localhost or blocking the port with a firewall. Stop gdbserver when it is not needed.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- crash
Version range not reported
- gdb
Version range not reported
- gdb
Version range not reported
- gdb
Version range not reported
- crash
Version range not reported
- gcc-toolset-14-gdb
Version range not reported
- gcc-toolset-15-gdb
Version range not reported
- gdb
Version range not reported
Show all 11 packagesShow fewer packages
- crash
Version range not reported
- gdb
Version range not reported
- gdb
Version range not reported
Evidence 2
- Report
- Link
Corrections
None so far.
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Questions about CVE-2026-121996
Is CVE-2026-121996 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
What does this mean?
A flaw in gdbserver's handling of agent expressions with an untrusted length lets a network client read uninitialized heap memory, which can include addresses useful for defeating ASLR, or crash gdbserver.Source: access.redhat.com
Am I affected, and how do I check?
This affects gdbserver as shipped with Red Hat Enterprise Linux 6, 7, 8, 9, and 10 and Red Hat Hardened Images, and only where the gdbserver port is reachable over the network. To check, look at the installed gdb package version and whether gdbserver is listening on a network-reachable port.Source: access.redhat.com
How do I fix CVE-2026-121996?
The checked facts do not list a fixed version, so no upgrade target is available from them. Follow Red Hat's advisory for the fixed package version.Source: access.redhat.com
What if there's no patch?
Until a fix is available, keep gdbserver ports off the network, for example by binding it to localhost or blocking the port with a firewall. Stop gdbserver when it is not needed.Source: access.redhat.com